diff --git a/.appveyor.yml b/.appveyor.yml
index 610ac134..d463b7a2 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -22,7 +22,7 @@ test_script:
   # Fetch and regenerate the fixture parsers
   - script\fetch-fixtures.cmd
   - cargo build --release
-  - script\regenerate-fixtures.cmd
+  - script\generate-fixtures.cmd
 
   # Run tests
   - script\test.cmd
diff --git a/.gitignore b/.gitignore
index 360390b1..ed31e54a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,6 +7,10 @@ fuzz-results
 
 test/fixtures/grammars/*
 !test/fixtures/grammars/.gitkeep
+package-lock.json
+node_modules
+
+docs/assets/js/tree-sitter.js
 
 /target
 *.rs.bk
@@ -15,3 +19,4 @@ test/fixtures/grammars/*
 *.obj
 *.exp
 *.lib
+*.wasm
diff --git a/.travis.yml b/.travis.yml
index 06c71b34..9fa65759 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,21 +2,33 @@ language: rust
 rust:
   - stable
 
-os:
-  - linux
-  - osx
+matrix:
+  include:
+    - os: osx
+    - os: linux
+      services: docker
+      env: TEST_WASM=1
+
+before_install:
+  # Install node
+  - if [ -n "$TEST_WASM" ]; then nvm install 10 && nvm use 10; fi
 
 script:
   # Fetch and regenerate the fixture parsers
   - script/fetch-fixtures
   - cargo build --release
-  - script/regenerate-fixtures
+  - script/generate-fixtures
 
-  # Run tests
+  # Run the tests
   - export TREE_SITTER_STATIC_ANALYSIS=1
   - script/test
   - script/benchmark
 
+  # Build and test the WASM binding
+  - if [ -n "$TEST_WASM" ]; then script/build-wasm; fi
+  - if [ -n "$TEST_WASM" ]; then script/generate-fixtures-wasm; fi
+  - if [ -n "$TEST_WASM" ]; then script/test-wasm; fi
+
 branches:
   only:
   - master
@@ -31,7 +43,10 @@ deploy:
   api_key:
     secure: "cAd2mQP+Q55v3zedo5ZyOVc3hq3XKMW93lp5LuXV6CYKYbIhkyfym4qfs+C9GJQiIP27cnePYM7B3+OMIFwSPIgXHWWSsuloMtDgYSc/PAwb2dZnJqAyog3BohW/QiGTSnvbVlxPF6P9RMQU6+JP0HJzEJy6QBTa4Und/j0jm24="
   file_glob: true
-  file: "tree-sitter-*.gz"
+  file:
+    - "tree-sitter-*.gz"
+    - "target/release/tree-sitter.js"
+    - "target/release/tree-sitter.wasm"
   draft: true
   overwrite: true
   skip_cleanup: true
diff --git a/cli/npm/package-lock.json b/cli/npm/package-lock.json
deleted file mode 100644
index ab7209ec..00000000
--- a/cli/npm/package-lock.json
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "name": "tree-sitter-cli",
-  "version": "0.15.1",
-  "lockfileVersion": 1
-}
diff --git a/cli/src/generate/mod.rs b/cli/src/generate/mod.rs
index 14c13aa4..48e747c9 100644
--- a/cli/src/generate/mod.rs
+++ b/cli/src/generate/mod.rs
@@ -15,7 +15,7 @@ mod grammars;
 mod nfa;
 mod node_types;
 mod npm_files;
-mod parse_grammar;
+pub mod parse_grammar;
 mod prepare_grammar;
 mod render;
 mod rules;
diff --git a/cli/src/generate/parse_grammar.rs b/cli/src/generate/parse_grammar.rs
index ce4b881a..feb560a9 100644
--- a/cli/src/generate/parse_grammar.rs
+++ b/cli/src/generate/parse_grammar.rs
@@ -64,8 +64,8 @@ enum RuleJSON {
 }
 
 #[derive(Deserialize)]
-struct GrammarJSON {
-    name: String,
+pub(crate) struct GrammarJSON {
+    pub(crate) name: String,
     rules: Map<String, Value>,
     conflicts: Option<Vec<Vec<String>>>,
     externals: Option<Vec<RuleJSON>>,
diff --git a/cli/src/lib.rs b/cli/src/lib.rs
index 19b82194..5d026cde 100644
--- a/cli/src/lib.rs
+++ b/cli/src/lib.rs
@@ -8,6 +8,7 @@ pub mod parse;
 pub mod properties;
 pub mod test;
 pub mod util;
+pub mod wasm;
 
 #[cfg(test)]
 mod tests;
diff --git a/cli/src/main.rs b/cli/src/main.rs
index a8b4fd8b..9decd720 100644
--- a/cli/src/main.rs
+++ b/cli/src/main.rs
@@ -5,7 +5,7 @@ use std::path::Path;
 use std::process::exit;
 use std::{u64, usize};
 use tree_sitter_cli::{
-    config, error, generate, highlight, loader, logger, parse, properties, test,
+    config, error, generate, highlight, loader, logger, parse, properties, test, wasm,
 };
 
 fn main() {
@@ -90,6 +90,11 @@ fn run() -> error::Result<()> {
                 .arg(Arg::with_name("html").long("html").short("h"))
                 .arg(Arg::with_name("time").long("time").short("t")),
         )
+        .subcommand(
+            SubCommand::with_name("build-wasm")
+                .about("Compile a parser to WASM")
+                .arg(Arg::with_name("path").index(1).multiple(true)),
+        )
         .get_matches();
 
     let home_dir = dirs::home_dir().expect("Failed to read home directory");
@@ -237,6 +242,9 @@ fn run() -> error::Result<()> {
                 )));
             }
         }
+    } else if let Some(matches) = matches.subcommand_matches("build-wasm") {
+        let grammar_path = current_dir.join(matches.value_of("path").unwrap_or(""));
+        wasm::compile_language_to_wasm(&grammar_path)?;
     }
 
     Ok(())
diff --git a/cli/src/tests/node_test.rs b/cli/src/tests/node_test.rs
index ebe404cd..a5fcaa3d 100644
--- a/cli/src/tests/node_test.rs
+++ b/cli/src/tests/node_test.rs
@@ -265,42 +265,90 @@ fn test_node_descendant_for_range() {
     let tree = parse_json_example();
     let array_node = tree.root_node().child(0).unwrap();
 
+    // Leaf node starts and ends at the given bounds - byte query
     let colon_index = JSON_EXAMPLE.find(":").unwrap();
-    let node1 = array_node
-        .descendant_for_byte_range(colon_index, colon_index)
+    let colon_node = array_node
+        .descendant_for_byte_range(colon_index, colon_index + 1)
         .unwrap();
-    assert_eq!(node1.kind(), ":");
-    assert_eq!(node1.start_byte(), colon_index);
-    assert_eq!(node1.end_byte(), colon_index + 1);
-    assert_eq!(node1.start_position(), Point::new(6, 7));
-    assert_eq!(node1.end_position(), Point::new(6, 8));
+    assert_eq!(colon_node.kind(), ":");
+    assert_eq!(colon_node.start_byte(), colon_index);
+    assert_eq!(colon_node.end_byte(), colon_index + 1);
+    assert_eq!(colon_node.start_position(), Point::new(6, 7));
+    assert_eq!(colon_node.end_position(), Point::new(6, 8));
 
+    // Leaf node starts and ends at the given bounds - point query
+    let colon_node = array_node
+        .descendant_for_point_range(Point::new(6, 7), Point::new(6, 8))
+        .unwrap();
+    assert_eq!(colon_node.kind(), ":");
+    assert_eq!(colon_node.start_byte(), colon_index);
+    assert_eq!(colon_node.end_byte(), colon_index + 1);
+    assert_eq!(colon_node.start_position(), Point::new(6, 7));
+    assert_eq!(colon_node.end_position(), Point::new(6, 8));
+
+    // Leaf node starts at the lower bound, ends after the upper bound - byte query
     let string_index = JSON_EXAMPLE.find("\"x\"").unwrap();
-    let node2 = array_node
+    let string_node = array_node
+        .descendant_for_byte_range(string_index, string_index + 2)
+        .unwrap();
+    assert_eq!(string_node.kind(), "string");
+    assert_eq!(string_node.start_byte(), string_index);
+    assert_eq!(string_node.end_byte(), string_index + 3);
+    assert_eq!(string_node.start_position(), Point::new(6, 4));
+    assert_eq!(string_node.end_position(), Point::new(6, 7));
+
+    // Leaf node starts at the lower bound, ends after the upper bound - point query
+    let string_node = array_node
+        .descendant_for_point_range(Point::new(6, 4), Point::new(6, 6))
+        .unwrap();
+    assert_eq!(string_node.kind(), "string");
+    assert_eq!(string_node.start_byte(), string_index);
+    assert_eq!(string_node.end_byte(), string_index + 3);
+    assert_eq!(string_node.start_position(), Point::new(6, 4));
+    assert_eq!(string_node.end_position(), Point::new(6, 7));
+
+    // Leaf node starts before the lower bound, ends at the upper bound - byte query
+    let null_index = JSON_EXAMPLE.find("null").unwrap();
+    let null_node = array_node
+        .descendant_for_byte_range(null_index + 1, null_index + 4)
+        .unwrap();
+    assert_eq!(null_node.kind(), "null");
+    assert_eq!(null_node.start_byte(), null_index);
+    assert_eq!(null_node.end_byte(), null_index + 4);
+    assert_eq!(null_node.start_position(), Point::new(6, 9));
+    assert_eq!(null_node.end_position(), Point::new(6, 13));
+
+    // Leaf node starts before the lower bound, ends at the upper bound - point query
+    let null_node = array_node
+        .descendant_for_point_range(Point::new(6, 11), Point::new(6, 13))
+        .unwrap();
+    assert_eq!(null_node.kind(), "null");
+    assert_eq!(null_node.start_byte(), null_index);
+    assert_eq!(null_node.end_byte(), null_index + 4);
+    assert_eq!(null_node.start_position(), Point::new(6, 9));
+    assert_eq!(null_node.end_position(), Point::new(6, 13));
+
+    // The bounds span multiple leaf nodes - return the smallest node that does span it.
+    let pair_node = array_node
         .descendant_for_byte_range(string_index + 2, string_index + 4)
         .unwrap();
-    assert_eq!(node2.kind(), "pair");
-    assert_eq!(node2.start_byte(), string_index);
-    assert_eq!(node2.end_byte(), string_index + 9);
-    assert_eq!(node2.start_position(), Point::new(6, 4));
-    assert_eq!(node2.end_position(), Point::new(6, 13));
+    assert_eq!(pair_node.kind(), "pair");
+    assert_eq!(pair_node.start_byte(), string_index);
+    assert_eq!(pair_node.end_byte(), string_index + 9);
+    assert_eq!(pair_node.start_position(), Point::new(6, 4));
+    assert_eq!(pair_node.end_position(), Point::new(6, 13));
 
-    assert_eq!(node1.parent(), Some(node2));
-
-    let node3 = array_node
-        .named_descendant_for_byte_range(string_index, string_index + 2)
-        .unwrap();
-    assert_eq!(node3.kind(), "string");
-    assert_eq!(node3.start_byte(), string_index);
-    assert_eq!(node3.end_byte(), string_index + 3);
+    assert_eq!(colon_node.parent(), Some(pair_node));
 
     // no leaf spans the given range - return the smallest node that does span it.
-    let node4 = array_node
-        .named_descendant_for_byte_range(string_index, string_index + 3)
+    let pair_node = array_node
+        .named_descendant_for_point_range(Point::new(6, 6), Point::new(6, 8))
         .unwrap();
-    assert_eq!(node4.kind(), "pair");
-    assert_eq!(node4.start_byte(), string_index);
-    assert_eq!(node4.end_byte(), string_index + 9);
+    assert_eq!(pair_node.kind(), "pair");
+    assert_eq!(pair_node.start_byte(), string_index);
+    assert_eq!(pair_node.end_byte(), string_index + 9);
+    assert_eq!(pair_node.start_position(), Point::new(6, 4));
+    assert_eq!(pair_node.end_position(), Point::new(6, 13));
 }
 
 #[test]
diff --git a/cli/src/wasm.rs b/cli/src/wasm.rs
new file mode 100644
index 00000000..1aaa1f61
--- /dev/null
+++ b/cli/src/wasm.rs
@@ -0,0 +1,99 @@
+use super::error::{Error, Result};
+use super::generate::parse_grammar::GrammarJSON;
+use std::ffi::{OsStr, OsString};
+use std::fs;
+use std::path::Path;
+use std::process::Command;
+
+pub fn compile_language_to_wasm(language_dir: &Path) -> Result<()> {
+    let src_dir = language_dir.join("src");
+
+    // Parse the grammar.json to find out the language name.
+    let grammar_json_path = src_dir.join("grammar.json");
+    let grammar_json = fs::read_to_string(&grammar_json_path).map_err(|e| {
+        format!(
+            "Failed to read grammar file {:?} - {}",
+            grammar_json_path, e
+        )
+    })?;
+    let grammar: GrammarJSON = serde_json::from_str(&grammar_json).map_err(|e| {
+        format!(
+            "Failed to parse grammar file {:?} - {}",
+            grammar_json_path, e
+        )
+    })?;
+    let output_filename = format!("tree-sitter-{}.wasm", grammar.name);
+
+    // Get the current user id so that files created in the docker container will have
+    // the same owner.
+    let user_id_output = Command::new("id")
+        .arg("-u")
+        .output()
+        .map_err(|e| format!("Failed to get get current user id {}", e))?;
+    let user_id = String::from_utf8_lossy(&user_id_output.stdout);
+    let user_id = user_id.trim();
+
+    // Use `emscripten-slim` docker image with the parser directory mounted as a volume.
+    let mut command = Command::new("docker");
+    let mut volume_string = OsString::from(language_dir);
+    volume_string.push(":/src");
+    command.args(&["run", "--rm"]);
+    command.args(&[OsStr::new("--volume"), &volume_string]);
+    command.args(&["--user", user_id, "trzeci/emscripten-slim"]);
+
+    // Run emscripten in the container
+    command.args(&[
+        "emcc",
+        "-o",
+        &output_filename,
+        "-Os",
+        "-s",
+        "WASM=1",
+        "-s",
+        "SIDE_MODULE=1",
+        "-s",
+        &format!("EXPORTED_FUNCTIONS=[\"_tree_sitter_{}\"]", grammar.name),
+        "-I",
+        "src",
+    ]);
+
+    // Find source files to pass to emscripten
+    let src_entries = fs::read_dir(&src_dir)
+        .map_err(|e| format!("Failed to read source directory {:?} - {}", src_dir, e))?;
+
+    for entry in src_entries {
+        let entry = entry?;
+        let file_name = entry.file_name();
+
+        // Do not compile the node.js binding file.
+        if file_name
+            .to_str()
+            .map_or(false, |s| s.starts_with("binding"))
+        {
+            continue;
+        }
+
+        // Compile any .c, .cc, or .cpp files
+        if let Some(extension) = Path::new(&file_name).extension().and_then(|s| s.to_str()) {
+            if extension == "c" || extension == "cc" || extension == "cpp" {
+                command.arg(Path::new("src").join(entry.file_name()));
+            }
+        }
+    }
+
+    let output = command
+        .output()
+        .map_err(|e| format!("Failed to run docker emcc command - {}", e))?;
+    if !output.status.success() {
+        return Err(Error::from(format!(
+            "emcc command failed - {}",
+            String::from_utf8_lossy(&output.stderr)
+        )));
+    }
+
+    // Move the created `.wasm` file into the current working directory.
+    fs::rename(&language_dir.join(&output_filename), &output_filename)
+        .map_err(|e| format!("Couldn't find output file {:?} - {}", output_filename, e))?;
+
+    Ok(())
+}
diff --git a/docs/_layouts/default.html b/docs/_layouts/default.html
index d000ad37..25be9c2d 100644
--- a/docs/_layouts/default.html
+++ b/docs/_layouts/default.html
@@ -130,7 +130,7 @@
     }
   });
 
-  $('h1, h2, h3').filter('[id]').each(function() {
+  $('h2, h3').filter('[id]').each(function() {
     $(this).html('<a href="#'+$(this).attr('id')+'">' + $(this).text() + '</a>');
   });
 </script>
diff --git a/docs/assets/css/style.scss b/docs/assets/css/style.scss
index 269cab34..57fe291d 100644
--- a/docs/assets/css/style.scss
+++ b/docs/assets/css/style.scss
@@ -116,3 +116,43 @@ body {
     }
   }
 }
+
+#playground-container {
+  > .CodeMirror {
+    height: auto;
+    max-height: 350px;
+    border: 1px solid #aaa;
+  }
+
+  .CodeMirror-scroll {
+    height: auto;
+    max-height: 350px;
+  }
+
+  h4, select, .field {
+    display: inline-block;
+    margin-right: 20px;
+  }
+
+  #logging-checkbox {
+    height: 15px;
+  }
+
+  .CodeMirror div.CodeMirror-cursor {
+    border-left: 3px solid red;
+  }
+}
+
+#output-container {
+  position: relative;
+  margin-top: 0;
+  overflow: auto;
+  padding: 20px 10px;
+  max-height: 350px;
+  border: 1px solid #aaa;
+}
+
+.tree-link.highlighted {
+  background-color: #ddd;
+  text-decoration: underline;
+}
diff --git a/docs/assets/js/playground.js b/docs/assets/js/playground.js
new file mode 100644
index 00000000..0b7e8127
--- /dev/null
+++ b/docs/assets/js/playground.js
@@ -0,0 +1,189 @@
+const codeInput = document.getElementById('code-input');
+const languageSelect = document.getElementById('language-select');
+const loggingCheckbox = document.getElementById('logging-checkbox');
+const outputContainer = document.getElementById('output-container');
+const updateTimeSpan = document.getElementById('update-time');
+const demoContainer = document.getElementById('playground-container');
+
+const languagesByName = {};
+
+let tree;
+let parser;
+let codeEditor;
+let queryEditor;
+let languageName;
+let highlightedNodeLink;
+
+main();
+
+async function main() {
+  await TreeSitter.init();
+  parser = new TreeSitter();
+  codeEditor = CodeMirror.fromTextArea(codeInput, {
+    lineNumbers: true,
+    showCursorWhenSelecting: true
+  });
+
+  languageName = languageSelect.value;
+  codeEditor.on('changes', handleCodeChange);
+  codeEditor.on('cursorActivity', handleCursorMovement);
+  loggingCheckbox.addEventListener('change', handleLoggingChange);
+  languageSelect.addEventListener('change', handleLanguageChange);
+  outputContainer.addEventListener('click', handleTreeClick);
+
+  await handleLanguageChange();
+  demoContainer.style.visibility = 'visible';
+}
+
+async function handleLanguageChange() {
+  const newLanguageName = languageSelect.value;
+  if (!languagesByName[newLanguageName]) {
+    const url = `${LANGUAGE_BASE_URL}/tree-sitter-${newLanguageName}.wasm`
+    languageSelect.disabled = true;
+    try {
+      languagesByName[newLanguageName] = await TreeSitter.Language.load(url);
+    } catch (e) {
+      console.error(e);
+      languageSelect.value = languageName;
+      return
+    } finally {
+      languageSelect.disabled = false;
+    }
+  }
+
+  tree = null;
+  languageName = newLanguageName;
+  parser.setLanguage(languagesByName[newLanguageName]);
+  handleCodeChange();
+}
+
+function handleLoggingChange() {
+  if (loggingCheckbox.checked) {
+    parser.setLogger(console.log);
+  } else {
+    parser.setLogger(null);
+  }
+}
+
+function handleCodeChange(editor, changes) {
+  let start;
+  if (tree && changes) {
+    start = performance.now();
+    for (const change of changes) {
+      const edit = treeEditForEditorChange(change);
+      tree.edit(edit);
+    }
+  } else {
+    start = performance.now();
+  }
+  const newTree = parser.parse(codeEditor.getValue() + '\n', tree);
+  tree && tree.delete();
+  tree = newTree;
+  updateTimeSpan.innerText = `${(performance.now() - start).toFixed(1)} ms`;
+  renderTree();
+}
+
+function handleTreeClick(event) {
+  if (event.target.className === 'tree-link') {
+    event.preventDefault();
+    const row = parseInt(event.target.dataset.row);
+    const column = parseInt(event.target.dataset.column);
+    codeEditor.setCursor({line: row, ch: column});
+    codeEditor.focus();
+  }
+}
+
+function treeEditForEditorChange(change) {
+  const oldLineCount = change.removed.length;
+  const newLineCount = change.text.length;
+  const lastLineLength = change.text[newLineCount - 1].length;
+
+  const startPosition = {row: change.from.line, column: change.from.ch};
+  const oldEndPosition = {row: change.to.line, column: change.to.ch};
+  const newEndPosition = {
+    row: startPosition.row + newLineCount - 1,
+    column: newLineCount === 1
+      ? startPosition.column + lastLineLength
+      : lastLineLength
+  };
+
+  const startIndex = codeEditor.indexFromPos(change.from);
+  let newEndIndex = startIndex + newLineCount - 1;
+  let oldEndIndex = startIndex + oldLineCount - 1;
+  for (let i = 0; i < newLineCount; i++) newEndIndex += change.text[i].length;
+  for (let i = 0; i < oldLineCount; i++) oldEndIndex += change.removed[i].length;
+
+  return {
+    startIndex, oldEndIndex, newEndIndex,
+    startPosition, oldEndPosition, newEndPosition
+  };
+}
+
+var handleCursorMovement = debounce(() => {
+  if (highlightedNodeLink) {
+    highlightedNodeLink.classList.remove('highlighted');
+    highlightedNodeLink = null;
+  }
+
+  const selection = codeEditor.getDoc().listSelections()[0];
+  let start = {row: selection.anchor.line, column: selection.anchor.ch};
+  let end = {row: selection.head.line, column: selection.head.ch};
+  if (
+    start.row > end.row ||
+    (
+      start.row === end.row &&
+      start.column > end.column
+    )
+  ) {
+    let swap = end;
+    end = start;
+    start = swap;
+  }
+  const node = tree.rootNode.namedDescendantForPosition(start, end);
+  const link = document.querySelector(`.tree-link[data-id="${node[0]}"]`);
+  link.classList.add('highlighted');
+  highlightedNodeLink = link;
+
+  $(outputContainer).animate({
+    scrollTop: Math.max(0, link.offsetTop - outputContainer.clientHeight / 2)
+  }, 200);
+}, 300);
+
+var renderTree = debounce(() => {
+  let result = "";
+  renderNode(tree.rootNode, 0);
+  function renderNode(node, indentLevel) {
+    let space = '  '.repeat(indentLevel);
+    const type = node.type;
+    const start = node.startPosition;
+    const end = node.endPosition;
+    result += space;
+    result += "(<a class='tree-link' href='#' ";
+    result += `data-id="${node[0]}" data-row=${start.row} data-column=${start.column}>${type}</a>`
+    result += `[${start.row + 1}, ${start.column}] - [${end.row + 1}, ${end.column}]`;
+    if (node.namedChildren.length > 0) {
+      for (let i = 0, n = node.namedChildren.length; i < n; i++) {
+        result += '\n';
+        renderNode(node.namedChildren[i], indentLevel + 1);
+      }
+    }
+    result += ')';
+  }
+
+  outputContainer.innerHTML = result;
+}, 200);
+
+function debounce(func, wait, immediate) {
+	var timeout;
+	return function() {
+		var context = this, args = arguments;
+		var later = function() {
+			timeout = null;
+			if (!immediate) func.apply(context, args);
+		};
+		var callNow = immediate && !timeout;
+		clearTimeout(timeout);
+		timeout = setTimeout(later, wait);
+		if (callNow) func.apply(context, args);
+	};
+};
diff --git a/docs/section-5-playground.html b/docs/section-5-playground.html
new file mode 100644
index 00000000..5a2bcdaf
--- /dev/null
+++ b/docs/section-5-playground.html
@@ -0,0 +1,60 @@
+---
+layout: default
+title: Playground
+permalink: playground
+---
+
+<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.45.0/codemirror.min.css">
+
+<h1>Playground</h1>
+
+<div id="playground-container" style="visibility: hidden;">
+
+<h4>Code</h4>
+<select id="language-select">
+  <option value="bash">Bash</option>
+  <option value="c">C</option>
+  <option value="cpp">C++</option>
+  <option value="go">Go</option>
+  <option value="html">HTML</option>
+  <option value="javascript" selected="selected">JavaScript</option>
+  <option value="python">Python</option>
+  <option value="ruby">Ruby</option>
+  <option value="rust">Rust</option>
+</select>
+
+<input id="logging-checkbox" type="checkbox"></input>
+<label for="logging-checkbox">Log</label>
+
+<textarea id="code-input">
+function quicksort() {
+  function sort(items) {
+    if (items.length <= 1) return items;
+    var pivot = items.shift(), current, left = [], right = [];
+    while (items.length > 0) {
+      current = items.shift();
+      current < pivot ? left.push(current) : right.push(current);
+    }
+    return sort(left).concat(pivot).concat(sort(right));
+  };
+  return sort(Array.apply(this, arguments));
+};
+</textarea>
+
+<h4>Tree</h4>
+<span id="update-time"></span>
+<pre id="output-container" class="highlight"></pre>
+
+</div>
+
+<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.45.0/codemirror.min.js"></script>
+
+{% if jekyll.environment == "development" %}
+<script>LANGUAGE_BASE_URL = "/assets/js";</script>
+<script src="/assets/js/tree-sitter.js"></script>
+{% else %}
+<script>LANGUAGE_BASE_URL = "https://tree-sitter.github.io";</script>
+<script src="https://tree-sitter.github.io/tree-sitter.js"></script>
+{% endif %}
+
+<script src="/assets/js/playground.js"></script>
diff --git a/lib/src/node.c b/lib/src/node.c
index e9796768..85139048 100644
--- a/lib/src/node.c
+++ b/lib/src/node.c
@@ -319,7 +319,7 @@ static inline TSNode ts_node__descendant_for_byte_range(TSNode self, uint32_t mi
     TSNode child;
     NodeChildIterator iterator = ts_node_iterate_children(&node);
     while (ts_node_child_iterator_next(&iterator, &child)) {
-      if (iterator.position.bytes > max) {
+      if (max <= iterator.position.bytes) {
         if (ts_node_start_byte(child) > min) break;
         node = child;
         if (ts_node__is_relevant(node, include_anonymous)) {
@@ -348,7 +348,7 @@ static inline TSNode ts_node__descendant_for_point_range(TSNode self, TSPoint mi
     TSNode child;
     NodeChildIterator iterator = ts_node_iterate_children(&node);
     while (ts_node_child_iterator_next(&iterator, &child)) {
-      if (point_gt(iterator.position.extent, max)) {
+      if (point_lte(max, iterator.position.extent)) {
         if (point_gt(ts_node_start_point(child), min)) break;
         node = child;
         if (ts_node__is_relevant(node, include_anonymous)) {
diff --git a/lib/web/binding.c b/lib/web/binding.c
new file mode 100644
index 00000000..748c91a6
--- /dev/null
+++ b/lib/web/binding.c
@@ -0,0 +1,343 @@
+#include <emscripten.h>
+#include <tree_sitter/api.h>
+#include <stdio.h>
+
+/*****************************/
+/* Section - Data marshaling */
+/*****************************/
+
+static const uint32_t INPUT_BUFFER_SIZE = 10 * 1024;
+
+const void *TRANSFER_BUFFER[12] = {
+  NULL, NULL, NULL, NULL,
+  NULL, NULL, NULL, NULL,
+  NULL, NULL, NULL, NULL,
+};
+
+void *ts_init() {
+  TRANSFER_BUFFER[0] = (const void *)TREE_SITTER_LANGUAGE_VERSION;
+  TRANSFER_BUFFER[1] = (const void *)TREE_SITTER_MIN_COMPATIBLE_LANGUAGE_VERSION;
+  return TRANSFER_BUFFER;
+}
+
+static uint32_t code_unit_to_byte(uint32_t unit) {
+  return unit << 1;
+}
+
+static uint32_t byte_to_code_unit(uint32_t byte) {
+  return byte >> 1;
+}
+
+static void marshal_node(const void **buffer, TSNode node) {
+  buffer[0] = (const void *)node.id;
+  buffer[1] = (const void *)node.context[0];
+  buffer[2] = (const void *)node.context[1];
+  buffer[3] = (const void *)node.context[2];
+  buffer[4] = (const void *)node.context[3];
+}
+
+static TSNode unmarshal_node(const TSTree *tree) {
+  TSNode node;
+  node.id = TRANSFER_BUFFER[0];
+  node.context[0] = (uint32_t)TRANSFER_BUFFER[1];
+  node.context[1] = (uint32_t)TRANSFER_BUFFER[2];
+  node.context[2] = (uint32_t)TRANSFER_BUFFER[3];
+  node.context[3] = (uint32_t)TRANSFER_BUFFER[4];
+  node.tree = tree;
+  return node;
+}
+
+static void marshal_point(TSPoint point) {
+  TRANSFER_BUFFER[0] = (const void *)point.row;
+  TRANSFER_BUFFER[1] = (const void *)byte_to_code_unit(point.column);
+}
+
+static TSPoint unmarshal_point(const void **address) {
+  TSPoint point;
+  point.row = (uint32_t)address[0];
+  point.column = code_unit_to_byte((uint32_t)address[1]);
+  return point;
+}
+
+static TSInputEdit unmarshal_edit() {
+  TSInputEdit edit;
+  const void **address = TRANSFER_BUFFER;
+  edit.start_point = unmarshal_point(address); address += 2;
+  edit.old_end_point = unmarshal_point(address); address += 2;
+  edit.new_end_point = unmarshal_point(address); address += 2;
+  edit.start_byte = code_unit_to_byte((uint32_t)*address); address += 1;
+  edit.old_end_byte = code_unit_to_byte((uint32_t)*address); address += 1;
+  edit.new_end_byte = code_unit_to_byte((uint32_t)*address); address += 1;
+  return edit;
+}
+
+/********************/
+/* Section - Parser */
+/********************/
+
+extern void tree_sitter_parse_callback(
+  char *input_buffer,
+  uint32_t index,
+  uint32_t row,
+  uint32_t column,
+  uint32_t *length_read
+);
+
+extern void tree_sitter_log_callback(
+  void *payload,
+  TSLogType log_type,
+  const char *message
+);
+
+void ts_parser_new_wasm() {
+  TSParser *parser = ts_parser_new();
+  char *input_buffer = calloc(INPUT_BUFFER_SIZE, sizeof(char));
+  TRANSFER_BUFFER[0] = parser;
+  TRANSFER_BUFFER[1] = input_buffer;
+}
+
+static const char *call_parse_callback(
+  void *payload,
+  uint32_t byte,
+  TSPoint position,
+  uint32_t *bytes_read
+) {
+  char *buffer = (char *)payload;
+  tree_sitter_parse_callback(
+    buffer,
+    byte_to_code_unit(byte),
+    position.row,
+    byte_to_code_unit(position.column),
+    bytes_read
+  );
+  *bytes_read = code_unit_to_byte(*bytes_read);
+  if (*bytes_read >= INPUT_BUFFER_SIZE) {
+    *bytes_read = INPUT_BUFFER_SIZE - 2;
+  }
+  return buffer;
+}
+
+void ts_parser_enable_logger_wasm(TSParser *self, bool should_log) {
+  TSLogger logger = {self, should_log ? tree_sitter_log_callback : NULL};
+  ts_parser_set_logger(self, logger);
+}
+
+TSTree *ts_parser_parse_wasm(
+  TSParser *self,
+  char *input_buffer,
+  const TSTree *old_tree,
+  TSRange *ranges,
+  uint32_t range_count
+) {
+  TSInput input = {
+    input_buffer,
+    call_parse_callback,
+    TSInputEncodingUTF16
+  };
+  if (range_count) {
+    for (unsigned i = 0; i < range_count; i++) {
+      TSRange *range = &ranges[i];
+      range->start_byte = code_unit_to_byte(range->start_byte);
+      range->end_byte = code_unit_to_byte(range->end_byte);
+      range->start_point.column = code_unit_to_byte(range->start_point.column);
+      range->end_point.column = code_unit_to_byte(range->end_point.column);
+    }
+    ts_parser_set_included_ranges(self, ranges, range_count);
+    free(ranges);
+  } else {
+    ts_parser_set_included_ranges(self, NULL, 0);
+  }
+  return ts_parser_parse(self, old_tree, input);
+}
+
+/******************/
+/* Section - Tree */
+/******************/
+
+void ts_tree_root_node_wasm(const TSTree *tree) {
+  marshal_node(TRANSFER_BUFFER, ts_tree_root_node(tree));
+}
+
+void ts_tree_edit_wasm(TSTree *tree) {
+  TSInputEdit edit = unmarshal_edit();
+  ts_tree_edit(tree, &edit);
+}
+
+/******************/
+/* Section - Node */
+/******************/
+
+static TSTreeCursor scratch_cursor = {0};
+
+uint16_t ts_node_symbol_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  return ts_node_symbol(node);
+}
+
+uint32_t ts_node_child_count_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  return ts_node_child_count(node);
+}
+
+uint32_t ts_node_named_child_count_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  return ts_node_named_child_count(node);
+}
+
+void ts_node_child_wasm(const TSTree *tree, uint32_t index) {
+  TSNode node = unmarshal_node(tree);
+  marshal_node(TRANSFER_BUFFER, ts_node_child(node, index));
+}
+
+void ts_node_named_child_wasm(const TSTree *tree, uint32_t index) {
+  TSNode node = unmarshal_node(tree);
+  marshal_node(TRANSFER_BUFFER, ts_node_named_child(node, index));
+}
+
+void ts_node_next_sibling_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  marshal_node(TRANSFER_BUFFER, ts_node_next_sibling(node));
+}
+
+void ts_node_prev_sibling_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  marshal_node(TRANSFER_BUFFER, ts_node_prev_sibling(node));
+}
+
+void ts_node_next_named_sibling_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  marshal_node(TRANSFER_BUFFER, ts_node_next_named_sibling(node));
+}
+
+void ts_node_prev_named_sibling_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  marshal_node(TRANSFER_BUFFER, ts_node_prev_named_sibling(node));
+}
+
+void ts_node_parent_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  marshal_node(TRANSFER_BUFFER, ts_node_parent(node));
+}
+
+void ts_node_descendant_for_index_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  const void **address = TRANSFER_BUFFER + 5;
+  uint32_t start = code_unit_to_byte((uint32_t)address[0]);
+  uint32_t end = code_unit_to_byte((uint32_t)address[1]);
+  marshal_node(TRANSFER_BUFFER, ts_node_descendant_for_byte_range(node, start, end));
+}
+
+void ts_node_named_descendant_for_index_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  const void **address = TRANSFER_BUFFER + 5;
+  uint32_t start = code_unit_to_byte((uint32_t)address[0]);
+  uint32_t end = code_unit_to_byte((uint32_t)address[1]);
+  marshal_node(TRANSFER_BUFFER, ts_node_named_descendant_for_byte_range(node, start, end));
+}
+
+void ts_node_descendant_for_position_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  const void **address = TRANSFER_BUFFER + 5;
+  TSPoint start = unmarshal_point(address); address += 2;
+  TSPoint end = unmarshal_point(address);
+  marshal_node(TRANSFER_BUFFER, ts_node_descendant_for_point_range(node, start, end));
+}
+
+void ts_node_named_descendant_for_position_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  const void **address = TRANSFER_BUFFER + 5;
+  TSPoint start = unmarshal_point(address); address += 2;
+  TSPoint end = unmarshal_point(address);
+  marshal_node(TRANSFER_BUFFER, ts_node_named_descendant_for_point_range(node, start, end));
+}
+
+void ts_node_start_point_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  marshal_point(ts_node_start_point(node));
+}
+
+void ts_node_end_point_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  marshal_point(ts_node_end_point(node));
+}
+
+uint32_t ts_node_start_index_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  return byte_to_code_unit(ts_node_start_byte(node));
+}
+
+uint32_t ts_node_end_index_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  return byte_to_code_unit(ts_node_end_byte(node));
+}
+
+char *ts_node_to_string_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  return ts_node_string(node);
+}
+
+void ts_node_children_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  uint32_t count = ts_node_child_count(node);
+  const void **result = NULL;
+  if (count > 0) {
+    result = calloc(sizeof(void *), 5 * count);
+    const void **address = result;
+    ts_tree_cursor_reset(&scratch_cursor, node);
+    ts_tree_cursor_goto_first_child(&scratch_cursor);
+    marshal_node(address, ts_tree_cursor_current_node(&scratch_cursor));
+    for (uint32_t i = 1; i < count; i++) {
+      address += 5;
+      ts_tree_cursor_goto_next_sibling(&scratch_cursor);
+      TSNode child = ts_tree_cursor_current_node(&scratch_cursor);
+      marshal_node(address, child);
+    }
+  }
+  TRANSFER_BUFFER[0] = (const void *)count;
+  TRANSFER_BUFFER[1] = result;
+}
+
+void ts_node_named_children_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  uint32_t count = ts_node_named_child_count(node);
+  const void **result = NULL;
+  if (count > 0) {
+    result = calloc(sizeof(void *), 5 * count);
+    const void **address = result;
+    ts_tree_cursor_reset(&scratch_cursor, node);
+    ts_tree_cursor_goto_first_child(&scratch_cursor);
+    uint32_t i = 0;
+    for (;;) {
+      TSNode child = ts_tree_cursor_current_node(&scratch_cursor);
+      if (ts_node_is_named(child)) {
+        marshal_node(address, child);
+        address += 5;
+        i++;
+        if (i == count) break;
+      }
+      if (!ts_tree_cursor_goto_next_sibling(&scratch_cursor)) break;
+    }
+  }
+  TRANSFER_BUFFER[0] = (const void *)count;
+  TRANSFER_BUFFER[1] = result;
+}
+
+int ts_node_is_named_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  return ts_node_is_named(node);
+}
+
+int ts_node_has_changes_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  return ts_node_has_changes(node);
+}
+
+int ts_node_has_error_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  return ts_node_has_error(node);
+}
+
+int ts_node_is_missing_wasm(const TSTree *tree) {
+  TSNode node = unmarshal_node(tree);
+  return ts_node_is_missing(node);
+}
diff --git a/lib/web/binding.js b/lib/web/binding.js
new file mode 100644
index 00000000..85bf1cb6
--- /dev/null
+++ b/lib/web/binding.js
@@ -0,0 +1,544 @@
+const C = Module;
+const INTERNAL = {};
+const SIZE_OF_INT = 4;
+const SIZE_OF_NODE = 5 * SIZE_OF_INT;
+const SIZE_OF_POINT = 2 * SIZE_OF_INT;
+const SIZE_OF_RANGE = 2 * SIZE_OF_INT + 2 * SIZE_OF_POINT;
+
+var VERSION;
+var MIN_COMPATIBLE_VERSION;
+var TRANSFER_BUFFER;
+var currentParseCallback;
+var currentLogCallback;
+var initPromise;
+
+class Parser {
+  static init() {
+    if (!initPromise) {
+      initPromise = new Promise(resolve => {
+        Module.onRuntimeInitialized = resolve
+      }).then(() => {
+        TRANSFER_BUFFER = C._ts_init();
+        VERSION = getValue(TRANSFER_BUFFER, 'i32');
+        MIN_COMPATIBLE_VERSION = getValue(TRANSFER_BUFFER + SIZE_OF_INT, 'i32');
+      });
+    }
+    return initPromise;
+  }
+
+  constructor() {
+    C._ts_parser_new_wasm();
+    this[0] = getValue(TRANSFER_BUFFER, 'i32');
+    this[1] = getValue(TRANSFER_BUFFER + SIZE_OF_INT, 'i32');
+  }
+
+  delete() {
+    C._ts_parser_delete(this[0]);
+    C._free(this[1]);
+  }
+
+  setLanguage(language) {
+    let address;
+    if (!language) {
+      address = 0;
+      language = null;
+    } else if (language.constructor === Language) {
+      address = language[0];
+      const version = C._ts_language_version(address);
+      if (version < MIN_COMPATIBLE_VERSION || VERSION < version) {
+        throw new Error(
+          `Incompatible language version ${version}. ` +
+          `Compatibility range ${MIN_COMPATIBLE_VERSION} through ${VERSION}.`
+        );
+      }
+    } else {
+      throw new Error('Argument must be a Language');
+    }
+    this.language = language;
+    C._ts_parser_set_language(this[0], address);
+    return this;
+  }
+
+  getLanguage() {
+    return this.language
+  }
+
+  parse(callback, oldTree, options) {
+    if (typeof callback === 'string') {
+      currentParseCallback = index => callback.slice(index);
+    } else if (typeof callback === 'function') {
+      currentParseCallback = callback;
+    } else {
+      throw new Error("Argument must be a string or a function");
+    }
+
+    if (this.logCallback) {
+      currentLogCallback = this.logCallback;
+      C._ts_parser_enable_logger_wasm(this[0], 1);
+    } else {
+      currentLogCallback = null;
+      C._ts_parser_enable_logger_wasm(this[0], 0);
+    }
+
+    let rangeCount = 0;
+    let rangeAddress = 0;
+    if (options && options.includedRanges) {
+      rangeCount = options.includedRanges.length;
+      rangeAddress = C._calloc(rangeCount, SIZE_OF_RANGE);
+      let address = rangeAddress;
+      for (let i = 0; i < rangeCount; i++) {
+        marshalRange(address, options.includedRanges[i]);
+        address += SIZE_OF_RANGE;
+      }
+    }
+
+    const treeAddress = C._ts_parser_parse_wasm(
+      this[0],
+      this[1],
+      oldTree ? oldTree[0] : 0,
+      rangeAddress,
+      rangeCount
+    );
+
+    if (!treeAddress) {
+      currentParseCallback = null;
+      currentLogCallback = null;
+      throw new Error('Parsing failed');
+    }
+
+    const result = new Tree(INTERNAL, treeAddress, this.language, currentParseCallback);
+    currentParseCallback = null;
+    currentLogCallback = null;
+    return result;
+  }
+
+  reset() {
+    C._ts_parser_parse_wasm(this[0]);
+  }
+
+  setTimeoutMicros(timeout) {
+    C._ts_parser_set_timeout_micros(this[0], timeout);
+  }
+
+  getTimeoutMicros(timeout) {
+    C._ts_parser_timeout_micros(this[0]);
+  }
+
+  setLogger(callback) {
+    if (!callback) {
+      callback = null;
+    } else if (typeof callback !== "function") {
+      throw new Error("Logger callback must be a function");
+    }
+    this.logCallback = callback;
+    return this;
+  }
+
+  getLogger() {
+    return this.logCallback;
+  }
+}
+
+class Tree {
+  constructor(internal, address, language, textCallback) {
+    if (internal !== INTERNAL) {
+      throw new Error('Illegal constructor')
+    }
+    this[0] = address;
+    this.language = language;
+    this.textCallback = textCallback;
+  }
+
+  copy() {
+    const address = C._ts_tree_copy(this[0]);
+    return new Tree(INTERNAL, address, this.language, this.textCallback);
+  }
+
+  delete() {
+    C._ts_tree_delete(this[0]);
+  }
+
+  edit(edit) {
+    marshalEdit(edit);
+    C._ts_tree_edit_wasm(this[0]);
+  }
+
+  get rootNode() {
+    C._ts_tree_root_node_wasm(this[0]);
+    return unmarshalNode(this);
+  }
+
+  getLanguage() {
+    return this.language;
+  }
+}
+
+class Node {
+  constructor(internal, tree) {
+    if (internal !== INTERNAL) {
+      throw new Error('Illegal constructor')
+    }
+    this.tree = tree;
+  }
+
+  get id() {
+    return this[0];
+  }
+
+  get typeId() {
+    marshalNode(this);
+    return C._ts_node_symbol_wasm(this.tree);
+  }
+
+  get type() {
+    return this.tree.language.types[this.typeId] || 'ERROR';
+  }
+
+  get startPosition() {
+    marshalNode(this);
+    C._ts_node_start_point_wasm(this.tree[0]);
+    return unmarshalPoint(TRANSFER_BUFFER);
+  }
+
+  get endPosition() {
+    marshalNode(this);
+    C._ts_node_end_point_wasm(this.tree[0]);
+    return unmarshalPoint(TRANSFER_BUFFER);
+  }
+
+  get startIndex() {
+    marshalNode(this);
+    return C._ts_node_start_index_wasm(this.tree[0]);
+  }
+
+  get endIndex() {
+    marshalNode(this);
+    return C._ts_node_end_index_wasm(this.tree[0]);
+  }
+
+  get text() {
+    const startIndex = this.startIndex;
+    const length = this.endIndex - startIndex;
+    let result = this.tree.textCallback(startIndex);
+    while (result.length < length) {
+      result += this.tree.textCallback(startIndex + result.length);
+    }
+    return result.slice(0, length);
+  }
+
+  isNamed() {
+    marshalNode(this);
+    return C._ts_node_is_named_wasm(this.tree[0]) === 1;
+  }
+
+  hasError() {
+    marshalNode(this);
+    return C._ts_node_has_error_wasm(this.tree[0]) === 1;
+  }
+
+  hasChanges() {
+    marshalNode(this);
+    return C._ts_node_has_changes_wasm(this.tree[0]) === 1;
+  }
+
+  isMissing() {
+    marshalNode(this);
+    return C._ts_node_is_missing_wasm(this.tree[0]) === 1;
+  }
+
+  equals(other) {
+    if (this === other) return true;
+    for (let i = 0; i < 5; i++) {
+      if (this[i] !== other[i]) return false;
+    }
+    return true;
+  }
+
+  child(index) {
+    marshalNode(this);
+    C._ts_node_child_wasm(this.tree[0], index);
+    return unmarshalNode(this.tree);
+  }
+
+  namedChild(index) {
+    marshalNode(this);
+    C._ts_node_named_child_wasm(this.tree[0], index);
+    return unmarshalNode(this.tree);
+  }
+
+  get childCount() {
+    marshalNode(this);
+    return C._ts_node_child_count_wasm(this.tree[0]);
+  }
+
+  get namedChildCount() {
+    marshalNode(this);
+    return C._ts_node_named_child_count_wasm(this.tree[0]);
+  }
+
+  get firstChild() {
+    return this.child(0);
+  }
+
+  get firstNamedChild() {
+    return this.namedChild(0);
+  }
+
+  get lastChild() {
+    return this.child(this.childCount - 1);
+  }
+
+  get lastNamedChild() {
+    return this.namedChild(this.namedChildCount - 1);
+  }
+
+  get children() {
+    if (!this._children) {
+      marshalNode(this);
+      C._ts_node_children_wasm(this.tree[0]);
+      const count = getValue(TRANSFER_BUFFER, 'i32');
+      const buffer = getValue(TRANSFER_BUFFER + SIZE_OF_INT, 'i32');
+      this._children = new Array(count);
+      if (count > 0) {
+        let address = buffer;
+        for (let i = 0; i < count; i++) {
+          this._children[i] = unmarshalNode(this.tree, address);
+          address += SIZE_OF_NODE;
+        }
+        C._free(buffer);
+      }
+    }
+    return this._children;
+  }
+
+  get namedChildren() {
+    if (!this._namedChildren) {
+      marshalNode(this);
+      C._ts_node_named_children_wasm(this.tree[0]);
+      const count = getValue(TRANSFER_BUFFER, 'i32');
+      const buffer = getValue(TRANSFER_BUFFER + SIZE_OF_INT, 'i32');
+      this._namedChildren = new Array(count);
+      if (count > 0) {
+        let address = buffer;
+        for (let i = 0; i < count; i++) {
+          this._namedChildren[i] = unmarshalNode(this.tree, address);
+          address += SIZE_OF_NODE;
+        }
+        C._free(buffer);
+      }
+    }
+    return this._namedChildren;
+  }
+
+  get nextSibling() {
+    marshalNode(this);
+    C._ts_node_next_sibling_wasm(this.tree[0]);
+    return unmarshalNode(this.tree);
+  }
+
+  get previousSibling() {
+    marshalNode(this);
+    C._ts_node_prev_sibling_wasm(this.tree[0]);
+    return unmarshalNode(this.tree);
+  }
+
+  get nextNamedSibling() {
+    marshalNode(this);
+    C._ts_node_next_named_sibling_wasm(this.tree[0]);
+    return unmarshalNode(this.tree);
+  }
+
+  get previousNamedSibling() {
+    marshalNode(this);
+    C._ts_node_prev_named_sibling_wasm(this.tree[0]);
+    return unmarshalNode(this.tree);
+  }
+
+  get parent() {
+    marshalNode(this);
+    C._ts_node_parent_wasm(this.tree[0]);
+    return unmarshalNode(this.tree);
+  }
+
+  descendantForIndex(start, end = start) {
+    if (typeof start !== 'number' || typeof end !== 'number') {
+      throw new Error('Arguments must be numbers');
+    }
+
+    marshalNode(this);
+    let address = TRANSFER_BUFFER + SIZE_OF_NODE;
+    setValue(address, start, 'i32');
+    setValue(address + SIZE_OF_INT, end, 'i32');
+    C._ts_node_descendant_for_index_wasm(this.tree[0]);
+    return unmarshalNode(this.tree);
+  }
+
+  namedDescendantForIndex(start, end = start) {
+    if (typeof start !== 'number' || typeof end !== 'number') {
+      throw new Error('Arguments must be numbers');
+    }
+
+    marshalNode(this);
+    let address = TRANSFER_BUFFER + SIZE_OF_NODE;
+    setValue(address, start, 'i32');
+    setValue(address + SIZE_OF_INT, end, 'i32');
+    C._ts_node_named_descendant_for_index_wasm(this.tree[0]);
+    return unmarshalNode(this.tree);
+  }
+
+  descendantForPosition(start, end = start) {
+    if (!isPoint(start) || !isPoint(end)) {
+      throw new Error('Arguments must be {row, column} objects');
+    }
+
+    marshalNode(this);
+    let address = TRANSFER_BUFFER + SIZE_OF_NODE;
+    marshalPoint(address, start);
+    marshalPoint(address + SIZE_OF_POINT, end);
+    C._ts_node_descendant_for_position_wasm(this.tree[0]);
+    return unmarshalNode(this.tree);
+  }
+
+  namedDescendantForPosition(start, end = start) {
+    if (!isPoint(start) || !isPoint(end)) {
+      throw new Error('Arguments must be {row, column} objects');
+    }
+
+    marshalNode(this);
+    let address = TRANSFER_BUFFER + SIZE_OF_NODE;
+    marshalPoint(address, start);
+    marshalPoint(address + SIZE_OF_POINT, end);
+    C._ts_node_named_descendant_for_position_wasm(this.tree[0]);
+    return unmarshalNode(this.tree);
+  }
+
+  toString() {
+    marshalNode(this);
+    const address = C._ts_node_to_string_wasm(this.tree[0]);
+    const result = AsciiToString(address);
+    C._free(address);
+    return result;
+  }
+}
+
+class Language {
+  constructor(internal, address) {
+    if (internal !== INTERNAL) {
+      throw new Error('Illegal constructor')
+    }
+    this[0] = address;
+    this.types = new Array(C._ts_language_symbol_count(this[0]));
+    for (let i = 0, n = this.types.length; i < n; i++) {
+      if (C._ts_language_symbol_type(this[0], i) < 2) {
+        this.types[i] = UTF8ToString(C._ts_language_symbol_name(this[0], i));
+      }
+    }
+  }
+
+  get version() {
+    return C._ts_language_version(this[0]);
+  }
+
+  static load(url) {
+    let bytes;
+    if (
+      typeof require === 'function' &&
+      require('url').parse(url).protocol == null
+    ) {
+      const fs = require('fs');
+      bytes = Promise.resolve(fs.readFileSync(url));
+    } else {
+      bytes = fetch(url)
+        .then(response => response.arrayBuffer()
+          .then(buffer => {
+            if (response.ok) {
+              return new Uint8Array(buffer);
+            } else {
+              const body = new TextDecoder('utf-8').decode(buffer);
+              throw new Error(`Language.load failed with status ${response.status}.\n\n${body}`)
+            }
+          }));
+    }
+
+    return bytes
+      .then(bytes => loadWebAssemblyModule(bytes, {loadAsync: true}))
+      .then(mod => {
+        const functionName = Object.keys(mod).find(key => key.includes("tree_sitter_"));
+        const languageAddress = mod[functionName]();
+        return new Language(INTERNAL, languageAddress);
+      });
+  }
+}
+
+function isPoint(point) {
+  return (
+    point &&
+    typeof point.row === 'number' &&
+    typeof point.row === 'number'
+  );
+}
+
+function marshalNode(node) {
+  let address = TRANSFER_BUFFER;
+  for (let i = 0; i < 5; i++) {
+    setValue(address, node[i], 'i32');
+    address += SIZE_OF_INT;
+  }
+}
+
+function unmarshalNode(tree, address = TRANSFER_BUFFER) {
+  const id = getValue(address, 'i32');
+  if (id === 0) return null;
+  const result = new Node(INTERNAL, tree);
+  result[0] = id;
+  address += SIZE_OF_INT;
+  for (let i = 1; i < 5; i++) {
+    result[i] = getValue(address, 'i32');
+    address += SIZE_OF_INT;
+  }
+  return result;
+}
+
+function marshalPoint(address, point) {
+  setValue(address, point.row, 'i32')
+  setValue(address + SIZE_OF_INT, point.column, 'i32')
+}
+
+function unmarshalPoint(address) {
+  return {
+    row: getValue(address, 'i32'),
+    column: getValue(address + SIZE_OF_INT, 'i32')
+  }
+}
+
+function marshalRange(address, range) {
+  marshalPoint(address, range.startPosition); address += SIZE_OF_POINT;
+  marshalPoint(address, range.endPosition); address += SIZE_OF_POINT;
+  setValue(address, range.startIndex, 'i32'); address += SIZE_OF_INT;
+  setValue(address, range.endIndex, 'i32'); address += SIZE_OF_INT;
+}
+
+function unmarshalRange(address) {
+  const result = {};
+  result.startPosition = unmarshalPoint(address); address += SIZE_OF_POINT;
+  result.endPosition = unmarshalPoint(address); address += SIZE_OF_POINT;
+  result.startIndex = getValue(address, 'i32'); address += SIZE_OF_INT;
+  result.endIndex = getValue(address, 'i32');
+  return result;
+}
+
+function marshalEdit(edit) {
+  let address = TRANSFER_BUFFER;
+  marshalPoint(address, edit.startPosition); address += SIZE_OF_POINT;
+  marshalPoint(address, edit.oldEndPosition); address += SIZE_OF_POINT;
+  marshalPoint(address, edit.newEndPosition); address += SIZE_OF_POINT;
+  setValue(address, edit.startIndex, 'i32'); address += SIZE_OF_INT;
+  setValue(address, edit.oldEndIndex, 'i32'); address += SIZE_OF_INT;
+  setValue(address, edit.newEndIndex, 'i32'); address += SIZE_OF_INT;
+}
+
+Parser.Language = Language;
+
+return Parser;
+
+}));
diff --git a/lib/web/imports.js b/lib/web/imports.js
new file mode 100644
index 00000000..ea34926f
--- /dev/null
+++ b/lib/web/imports.js
@@ -0,0 +1,25 @@
+mergeInto(LibraryManager.library, {
+  tree_sitter_parse_callback: function(
+    inputBufferAddress,
+    index,
+    row,
+    column,
+    lengthAddress
+  ) {
+    var INPUT_BUFFER_SIZE = 10 * 1024;
+    var string = currentParseCallback(index, {row: row, column: column});
+    if (typeof string === 'string') {
+      setValue(lengthAddress, string.length, 'i32');
+      stringToUTF16(string, inputBufferAddress, INPUT_BUFFER_SIZE);
+    } else {
+      setValue(lengthAddress, 0, 'i32');
+    }
+  },
+
+  tree_sitter_log_callback: function(_payload, isLexMessage, messageAddress) {
+    if (currentLogCallback) {
+      const message = UTF8ToString(messageAddress);
+      currentLogCallback(message, isLexMessage !== 0);
+    }
+  }
+});
diff --git a/lib/web/package.json b/lib/web/package.json
new file mode 100644
index 00000000..9f0b60bc
--- /dev/null
+++ b/lib/web/package.json
@@ -0,0 +1,31 @@
+{
+  "name": "tree-sitter.wasm",
+  "version": "0.0.1",
+  "description": "Tree-sitter bindings for the web",
+  "main": "index.js",
+  "directories": {
+    "test": "test"
+  },
+  "scripts": {
+    "test": "mocha"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/tree-sitter/tree-sitter.git"
+  },
+  "keywords": [
+    "incremental",
+    "parsing"
+  ],
+  "author": "Max Brunsfeld",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/tree-sitter/tree-sitter/issues"
+  },
+  "homepage": "https://github.com/tree-sitter/tree-sitter#readme",
+  "devDependencies": {
+    "chai": "^4.2.0",
+    "mocha": "^6.1.4",
+    "terser": "^3.17.0"
+  }
+}
diff --git a/lib/web/prefix.js b/lib/web/prefix.js
new file mode 100644
index 00000000..ccd94fa4
--- /dev/null
+++ b/lib/web/prefix.js
@@ -0,0 +1,11 @@
+(function (root, factory) {
+  if (typeof define === 'function' && define.amd) {
+    define([], factory);
+  } else if (typeof exports === 'object') {
+    module.exports = factory();
+    // module.exports.init();
+    // delete module.exports.init;
+  } else {
+    window.TreeSitter = factory();
+  }
+}(this, function () {
diff --git a/lib/web/test/helper.js b/lib/web/test/helper.js
new file mode 100644
index 00000000..6586f247
--- /dev/null
+++ b/lib/web/test/helper.js
@@ -0,0 +1,8 @@
+const release = '../../../target/release'
+const Parser = require(`${release}/tree-sitter.js`);
+const JavaScript = require.resolve(`${release}/tree-sitter-javascript.wasm`);
+
+module.exports = Parser.init().then(async () => ({
+  Parser,
+  JavaScript: await Parser.Language.load(JavaScript),
+}));
diff --git a/lib/web/test/node-test.js b/lib/web/test/node-test.js
new file mode 100644
index 00000000..5d5716f9
--- /dev/null
+++ b/lib/web/test/node-test.js
@@ -0,0 +1,358 @@
+const {assert} = require('chai');
+let Parser, JavaScript;
+
+describe("Node", () => {
+  let parser, tree;
+
+  before(async () =>
+    ({Parser, JavaScript} = await require('./helper'))
+  );
+
+  beforeEach(() => {
+    tree = null;
+    parser = new Parser().setLanguage(JavaScript);
+  });
+
+  afterEach(() => {
+    parser.delete();
+    tree.delete();
+  });
+
+  describe(".children", () => {
+    it("returns an array of child nodes", () => {
+      tree = parser.parse("x10 + 1000");
+      assert.equal(1, tree.rootNode.children.length);
+      const sumNode = tree.rootNode.firstChild.firstChild;
+      assert.deepEqual(
+        sumNode.children.map(child => child.type),
+        ["identifier", "+", "number"]
+      );
+    });
+  });
+
+  describe(".namedChildren", () => {
+    it("returns an array of named child nodes", () => {
+      tree = parser.parse("x10 + 1000");
+      const sumNode = tree.rootNode.firstChild.firstChild;
+      assert.equal(1, tree.rootNode.namedChildren.length);
+      assert.deepEqual(
+        ["identifier", "number"],
+        sumNode.namedChildren.map(child => child.type)
+      );
+    });
+  });
+
+  describe(".startIndex and .endIndex", () => {
+    it("returns the character index where the node starts/ends in the text", () => {
+      tree = parser.parse("a👍👎1 / b👎c👎");
+      const quotientNode = tree.rootNode.firstChild.firstChild;
+
+      assert.equal(0, quotientNode.startIndex);
+      assert.equal(15, quotientNode.endIndex);
+      assert.deepEqual(
+        [0, 7, 9],
+        quotientNode.children.map(child => child.startIndex)
+      );
+      assert.deepEqual(
+        [6, 8, 15],
+        quotientNode.children.map(child => child.endIndex)
+      );
+    });
+  });
+
+  describe(".startPosition and .endPosition", () => {
+    it("returns the row and column where the node starts/ends in the text", () => {
+      tree = parser.parse("x10 + 1000");
+      const sumNode = tree.rootNode.firstChild.firstChild;
+      assert.equal("binary_expression", sumNode.type);
+
+      assert.deepEqual({ row: 0, column: 0 }, sumNode.startPosition);
+      assert.deepEqual({ row: 0, column: 10 }, sumNode.endPosition);
+      assert.deepEqual(
+        [{ row: 0, column: 0 }, { row: 0, column: 4 }, { row: 0, column: 6 }],
+        sumNode.children.map(child => child.startPosition)
+      );
+      assert.deepEqual(
+        [{ row: 0, column: 3 }, { row: 0, column: 5 }, { row: 0, column: 10 }],
+        sumNode.children.map(child => child.endPosition)
+      );
+    });
+
+    it("handles characters that occupy two UTF16 code units", () => {
+      tree = parser.parse("a👍👎1 /\n b👎c👎");
+      const sumNode = tree.rootNode.firstChild.firstChild;
+      assert.deepEqual(
+        [
+          [{ row: 0, column: 0 }, { row: 0, column: 6 }],
+          [{ row: 0, column: 7 }, { row: 0, column: 8 }],
+          [{ row: 1, column: 1 }, { row: 1, column: 7 }]
+        ],
+        sumNode.children.map(child => [child.startPosition, child.endPosition])
+      );
+    });
+  });
+
+  describe(".parent", () => {
+    it("returns the node's parent", () => {
+      tree = parser.parse("x10 + 1000");
+      const sumNode = tree.rootNode.firstChild;
+      const variableNode = sumNode.firstChild;
+      assert.notEqual(sumNode.id, variableNode.id);
+      assert.equal(sumNode.id, variableNode.parent.id);
+      assert.equal(tree.rootNode.id, sumNode.parent.id);
+    });
+  });
+
+  describe('.child(), .firstChild, .lastChild', () => {
+    it('returns null when the node has no children', () => {
+      tree = parser.parse("x10 + 1000");
+      const sumNode = tree.rootNode.firstChild.firstChild;
+      const variableNode = sumNode.firstChild;
+      assert.equal(variableNode.firstChild, null);
+      assert.equal(variableNode.lastChild, null);
+      assert.equal(variableNode.firstNamedChild, null);
+      assert.equal(variableNode.lastNamedChild, null);
+      assert.equal(variableNode.child(1), null);
+    })
+  });
+
+  describe(".nextSibling and .previousSibling", () => {
+    it("returns the node's next and previous sibling", () => {
+      tree = parser.parse("x10 + 1000");
+      const sumNode = tree.rootNode.firstChild.firstChild;
+      assert.equal(sumNode.children[1].id, sumNode.children[0].nextSibling.id);
+      assert.equal(sumNode.children[2].id, sumNode.children[1].nextSibling.id);
+      assert.equal(
+        sumNode.children[0].id,
+        sumNode.children[1].previousSibling.id
+      );
+      assert.equal(
+        sumNode.children[1].id,
+        sumNode.children[2].previousSibling.id
+      );
+    });
+  });
+
+  describe(".nextNamedSibling and .previousNamedSibling", () => {
+    it("returns the node's next and previous named sibling", () => {
+      tree = parser.parse("x10 + 1000");
+      const sumNode = tree.rootNode.firstChild.firstChild;
+      assert.equal(
+        sumNode.namedChildren[1].id,
+        sumNode.namedChildren[0].nextNamedSibling.id
+      );
+      assert.equal(
+        sumNode.namedChildren[0].id,
+        sumNode.namedChildren[1].previousNamedSibling.id
+      );
+    });
+  });
+
+  describe(".descendantForIndex(min, max)", () => {
+    it("returns the smallest node that spans the given range", () => {
+      tree = parser.parse("x10 + 1000");
+      const sumNode = tree.rootNode.firstChild.firstChild;
+      assert.equal("identifier", sumNode.descendantForIndex(1, 2).type);
+      assert.equal("+", sumNode.descendantForIndex(4, 4).type);
+
+      assert.throws(() => {
+        sumNode.descendantForIndex(1, {});
+      }, "Arguments must be numbers");
+
+      assert.throws(() => {
+        sumNode.descendantForIndex();
+      }, "Arguments must be numbers");
+    });
+  });
+
+  describe(".namedDescendantForIndex", () => {
+    it("returns the smallest node that spans the given range", () => {
+      tree = parser.parse("x10 + 1000");
+      const sumNode = tree.rootNode.firstChild;
+      assert.equal("identifier", sumNode.descendantForIndex(1, 2).type);
+      assert.equal("+", sumNode.descendantForIndex(4, 4).type);
+    });
+  });
+
+  describe(".descendantForPosition(min, max)", () => {
+    it("returns the smallest node that spans the given range", () => {
+      tree = parser.parse("x10 + 1000");
+      const sumNode = tree.rootNode.firstChild;
+
+      assert.equal(
+        "identifier",
+        sumNode.descendantForPosition(
+          { row: 0, column: 1 },
+          { row: 0, column: 2 }
+        ).type
+      );
+
+      assert.equal(
+        "+",
+        sumNode.descendantForPosition({ row: 0, column: 4 }).type
+      );
+
+      assert.throws(() => {
+        sumNode.descendantForPosition(1, {});
+      }, "Arguments must be {row, column} objects");
+
+      assert.throws(() => {
+        sumNode.descendantForPosition();
+      }, "Arguments must be {row, column} objects");
+    });
+  });
+
+  describe(".namedDescendantForPosition(min, max)", () => {
+    it("returns the smallest named node that spans the given range", () => {
+      tree = parser.parse("x10 + 1000");
+      const sumNode = tree.rootNode.firstChild;
+
+      assert.equal(
+        sumNode.namedDescendantForPosition(
+          { row: 0, column: 1 },
+          { row: 0, column: 2 }
+        ).type,
+        "identifier",
+      );
+
+      assert.equal(
+        sumNode.namedDescendantForPosition({ row: 0, column: 4 }).type,
+        'binary_expression'
+      );
+    });
+  });
+
+  describe(".hasError()", () => {
+    it("returns true if the node contains an error", () => {
+      tree = parser.parse("1 + 2 * * 3");
+      const node = tree.rootNode;
+      assert.equal(
+        node.toString(),
+        '(program (expression_statement (binary_expression (number) (binary_expression (number) (ERROR) (number)))))'
+      );
+
+      const sum = node.firstChild.firstChild;
+      assert(sum.hasError());
+      assert(!sum.children[0].hasError());
+      assert(!sum.children[1].hasError());
+      assert(sum.children[2].hasError());
+    });
+  });
+
+  describe(".isMissing()", () => {
+    it("returns true if the node is missing from the source and was inserted via error recovery", () => {
+      tree = parser.parse("(2 ||)");
+      const node = tree.rootNode;
+      assert.equal(
+        node.toString(),
+        "(program (expression_statement (parenthesized_expression (binary_expression (number) (MISSING identifier)))))"
+      );
+
+      const sum = node.firstChild.firstChild.firstNamedChild;
+      assert.equal(sum.type, 'binary_expression')
+      assert(sum.hasError());
+      assert(!sum.children[0].isMissing());
+      assert(!sum.children[1].isMissing());
+      assert(sum.children[2].isMissing());
+    });
+  });
+
+  describe(".text", () => {
+    const text = "α0 / b👎c👎";
+
+    Object.entries({
+      '.parse(String)': text,
+      '.parse(Function)': offset => text.substr(offset, 4)
+    }).forEach(([method, parse]) =>
+      it(`returns the text of a node generated by ${method}`, async () => {
+        const [numeratorSrc, denominatorSrc] = text.split(/\s*\/\s+/)
+        tree = await parser.parse(text)
+        const quotientNode = tree.rootNode.firstChild.firstChild;
+        const [numerator, slash, denominator] = quotientNode.children;
+
+        assert.equal(text, tree.rootNode.text,          'root node text');
+        assert.equal(denominatorSrc, denominator.text, 'denominator text');
+        assert.equal(text, quotientNode.text,           'quotient text');
+        assert.equal(numeratorSrc, numerator.text,     'numerator text');
+        assert.equal('/', slash.text,                  '"/" text');
+      })
+    );
+  });
+
+  describe.skip('.descendantsOfType(type, min, max)', () => {
+    it('finds all of the descendants of the given type in the given range', () => {
+      tree = parser.parse("a + 1 * b * 2 + c + 3");
+      const outerSum = tree.rootNode.firstChild.firstChild;
+      let descendants = outerSum.descendantsOfType('number', {row: 0, column: 2}, {row: 0, column: 15})
+      assert.deepEqual(
+        descendants.map(node => node.startIndex),
+        [4, 12]
+      );
+
+      descendants = outerSum.descendantsOfType('identifier', {row: 0, column: 2}, {row: 0, column: 15})
+      assert.deepEqual(
+        descendants.map(node => node.startIndex),
+        [8]
+      );
+
+      descendants = outerSum.descendantsOfType('identifier', {row: 0, column: 0}, {row: 0, column: 30})
+      assert.deepEqual(
+        descendants.map(node => node.startIndex),
+        [0, 8, 16]
+      );
+
+      descendants = outerSum.descendantsOfType('number', {row: 0, column: 0}, {row: 0, column: 30})
+      assert.deepEqual(
+        descendants.map(node => node.startIndex),
+        [4, 12, 20]
+      );
+
+      descendants = outerSum.descendantsOfType(
+        ['identifier', 'number'],
+        {row: 0, column: 0},
+        {row: 0, column: 30}
+      )
+      assert.deepEqual(
+        descendants.map(node => node.startIndex),
+        [0, 4, 8, 12, 16, 20]
+      );
+
+      descendants = outerSum.descendantsOfType('number')
+      assert.deepEqual(
+        descendants.map(node => node.startIndex),
+        [4, 12, 20]
+      );
+
+      descendants = outerSum.firstChild.descendantsOfType('number', {row: 0, column: 0}, {row: 0, column: 30})
+      assert.deepEqual(
+        descendants.map(node => node.startIndex),
+        [4, 12]
+      );
+    })
+  });
+
+  describe.skip('.closest(type)', () => {
+    it('returns the closest ancestor of the given type', () => {
+      tree = parser.parse("a(b + -d.e)");
+      const property = tree.rootNode.descendantForIndex("a(b + -d.".length);
+      assert.equal(property.type, 'property_identifier');
+
+      const unary = property.closest('unary_expression')
+      assert.equal(unary.type, 'unary_expression')
+      assert.equal(unary.startIndex, 'a(b + '.length)
+      assert.equal(unary.endIndex, 'a(b + -d.e'.length)
+
+      const sum = property.closest(['binary_expression', 'call_expression'])
+      assert.equal(sum.type, 'binary_expression')
+      assert.equal(sum.startIndex, 2)
+      assert.equal(sum.endIndex, 'a(b + -d.e'.length)
+    });
+
+    it('throws an exception when an invalid argument is given', () => {
+      tree = parser.parse("a + 1 * b * 2 + c + 3");
+      const number = tree.rootNode.descendantForIndex(4)
+
+      assert.throws(() => number.closest({a: 1}), /Argument must be a string or array of strings/)
+    });
+  });
+});
diff --git a/lib/web/test/parser-test.js b/lib/web/test/parser-test.js
new file mode 100644
index 00000000..991efc73
--- /dev/null
+++ b/lib/web/test/parser-test.js
@@ -0,0 +1,158 @@
+const {assert} = require('chai');
+let Parser, JavaScript;
+
+describe("Parser", () => {
+  let parser;
+
+  before(async () =>
+    ({Parser, JavaScript} = await require('./helper'))
+  );
+
+  beforeEach(() => {
+    parser = new Parser();
+  });
+
+  afterEach(() => {
+    parser.delete()
+  });
+
+  describe(".setLanguage", () => {
+    it("allows setting the language to null", () => {
+      assert.equal(parser.getLanguage(), null);
+      parser.setLanguage(JavaScript);
+      assert.equal(parser.getLanguage(), JavaScript);
+      parser.setLanguage(null);
+      assert.equal(parser.getLanguage(), null);
+    });
+
+    it("throws an exception when the given object is not a tree-sitter language", () => {
+      assert.throws(() => parser.setLanguage({}), /Argument must be a Language/);
+      assert.throws(() => parser.setLanguage(1), /Argument must be a Language/);
+    });
+  });
+
+  describe(".setLogger", () => {
+    beforeEach(() => {
+      parser.setLanguage(JavaScript)
+    });
+
+    it("calls the given callback for each parse event", () => {
+      const debugMessages = [];
+      parser.setLogger((message) => debugMessages.push(message));
+      parser.parse("a + b + c");
+      assert.includeMembers(debugMessages, [
+        "skip character:' '",
+        "consume character:'b'",
+        "reduce sym:program, child_count:1",
+        "accept"
+      ]);
+    });
+
+    it("allows the callback to be retrieved later", () => {
+      const callback = () => {}
+      parser.setLogger(callback);
+      assert.equal(parser.getLogger(), callback);
+      parser.setLogger(false);
+      assert.equal(parser.getLogger(), null);
+    });
+
+    it("disables debugging when given a falsy value", () => {
+      const debugMessages = [];
+      parser.setLogger((message) => debugMessages.push(message));
+      parser.setLogger(false);
+      parser.parse("a + b * c");
+      assert.equal(debugMessages.length, 0);
+    });
+
+    it("throws an error when given a truthy value that isn't a function ", () => {
+      assert.throws(
+        () => parser.setLogger("5"),
+        "Logger callback must be a function"
+      );
+    });
+
+    it("rethrows errors thrown by the logging callback", () => {
+      const error = new Error("The error message");
+      parser.setLogger((msg, params) => { throw error; });
+      assert.throws(
+        () => parser.parse("ok;"),
+        "The error message"
+      );
+    });
+  });
+
+  describe(".parse", () => {
+    let tree;
+
+    beforeEach(() => {
+      tree = null;
+      parser.setLanguage(JavaScript)
+    });
+
+    afterEach(() => {
+      if (tree) tree.delete();
+    });
+
+    it("reads from the given input", () => {
+      const parts = ["first", "_", "second", "_", "third"];
+      tree = parser.parse(() => parts.shift());
+      assert.equal(tree.rootNode.toString(), "(program (expression_statement (identifier)))");
+    });
+
+    it("stops reading when the input callback return something that's not a string", () => {
+      const parts = ["abc", "def", "ghi", {}, {}, {}, "second-word", " "];
+      tree = parser.parse(() => parts.shift());
+      assert.equal(
+        tree.rootNode.toString(),
+        "(program (expression_statement (identifier)))"
+      );
+      assert.equal(tree.rootNode.endIndex, 9);
+      assert.equal(parts.length, 2);
+    });
+
+    it("throws an exception when the given input is not a function", () => {
+      assert.throws(() => parser.parse(null), "Argument must be a string or a function");
+      assert.throws(() => parser.parse(5), "Argument must be a string or a function");
+      assert.throws(() => parser.parse({}), "Argument must be a string or a function");
+    });
+
+    it("handles long input strings", () => {
+      const repeatCount = 10000;
+      const inputString = "[" + "0,".repeat(repeatCount) + "]";
+
+      tree = parser.parse(inputString);
+      assert.equal(tree.rootNode.type, "program");
+      assert.equal(tree.rootNode.firstChild.firstChild.namedChildCount, repeatCount);
+    });
+
+    it('parses only the text within the `includedRanges` if they are specified', () => {
+      const sourceCode = "<% foo() %> <% bar %>";
+
+      const start1 = sourceCode.indexOf('foo');
+      const end1 = start1 + 5
+      const start2 = sourceCode.indexOf('bar');
+      const end2 = start2 + 3
+
+      const tree = parser.parse(sourceCode, null, {
+        includedRanges: [
+          {
+            startIndex: start1,
+            endIndex: end1,
+            startPosition: {row: 0, column: start1},
+            endPosition: {row: 0, column: end1}
+          },
+          {
+            startIndex: start2,
+            endIndex: end2,
+            startPosition: {row: 0, column: start2},
+            endPosition: {row: 0, column: end2}
+          },
+        ]
+      });
+
+      assert.equal(
+        tree.rootNode.toString(),
+        '(program (expression_statement (call_expression (identifier) (arguments))) (expression_statement (identifier)))'
+      );
+    })
+  });});
diff --git a/lib/web/test/tree-test.js b/lib/web/test/tree-test.js
new file mode 100644
index 00000000..ea7f085f
--- /dev/null
+++ b/lib/web/test/tree-test.js
@@ -0,0 +1,112 @@
+const {assert} = require('chai');
+let Parser, JavaScript;
+
+describe("Tree", () => {
+  let parser, tree;
+
+  before(async () =>
+    ({Parser, JavaScript} = await require('./helper'))
+  );
+
+  beforeEach(() => {
+    parser = new Parser().setLanguage(JavaScript);
+  });
+
+  afterEach(() => {
+    parser.delete();
+    tree.delete();
+  });
+
+  describe('.edit', () => {
+    let input, edit
+
+    it('updates the positions of nodes', () => {
+      parser.setLanguage(JavaScript)
+
+      input = 'abc + cde';
+      tree = parser.parse(input);
+      assert.equal(
+        tree.rootNode.toString(),
+        "(program (expression_statement (binary_expression (identifier) (identifier))))"
+      );
+
+      let sumNode = tree.rootNode.firstChild.firstChild;
+      let variableNode1 = sumNode.firstChild;
+      let variableNode2 = sumNode.lastChild;
+      assert.equal(variableNode1.startIndex, 0);
+      assert.equal(variableNode1.endIndex, 3);
+      assert.equal(variableNode2.startIndex, 6);
+      assert.equal(variableNode2.endIndex, 9);
+
+      ([input, edit] = spliceInput(input, input.indexOf('bc'), 0, ' * '));
+      assert.equal(input, 'a * bc + cde');
+      tree.edit(edit);
+
+      sumNode = tree.rootNode.firstChild.firstChild;
+      variableNode1 = sumNode.firstChild;
+      variableNode2 = sumNode.lastChild;
+      assert.equal(variableNode1.startIndex, 0);
+      assert.equal(variableNode1.endIndex, 6);
+      assert.equal(variableNode2.startIndex, 9);
+      assert.equal(variableNode2.endIndex, 12);
+
+      tree = parser.parse(input, tree);
+      assert.equal(
+        tree.rootNode.toString(),
+        "(program (expression_statement (binary_expression (binary_expression (identifier) (identifier)) (identifier))))"
+      );
+    });
+
+    it("handles non-ascii characters", () => {
+      input = 'αβδ + cde';
+
+      tree = parser.parse(input);
+      assert.equal(
+        tree.rootNode.toString(),
+        "(program (expression_statement (binary_expression (identifier) (identifier))))"
+      );
+
+      let variableNode = tree.rootNode.firstChild.firstChild.lastChild;
+
+      ([input, edit] = spliceInput(input, input.indexOf('δ'), 0, '👍 * '));
+      assert.equal(input, 'αβ👍 * δ + cde');
+      tree.edit(edit);
+
+      variableNode = tree.rootNode.firstChild.firstChild.lastChild;
+      assert.equal(variableNode.startIndex, input.indexOf('cde'));
+
+      tree = parser.parse(input, tree);
+      assert.equal(
+        tree.rootNode.toString(),
+        "(program (expression_statement (binary_expression (binary_expression (identifier) (identifier)) (identifier))))"
+      );
+    });
+  });
+});
+
+function spliceInput(input, startIndex, lengthRemoved, newText) {
+  const oldEndIndex = startIndex + lengthRemoved;
+  const newEndIndex = startIndex + newText.length;
+  const startPosition = getExtent(input.slice(0, startIndex));
+  const oldEndPosition = getExtent(input.slice(0, oldEndIndex));
+  input = input.slice(0, startIndex) + newText + input.slice(oldEndIndex);
+  const newEndPosition = getExtent(input.slice(0, newEndIndex));
+  return [
+    input,
+    {
+      startIndex, startPosition,
+      oldEndIndex, oldEndPosition,
+      newEndIndex, newEndPosition
+    }
+  ];
+}
+
+function getExtent(text) {
+  let row = 0
+  let index;
+  for (index = 0; index != -1; index = text.indexOf('\n', index)) {
+    index++
+    row++;
+  }
+  return {row, column: text.length - index};
+}
diff --git a/script/build-wasm b/script/build-wasm
new file mode 100755
index 00000000..819c601f
--- /dev/null
+++ b/script/build-wasm
@@ -0,0 +1,53 @@
+#!/usr/bin/env bash
+
+set -e
+
+export EMCC_FORCE_STDLIBS=libc++
+
+args="-Os"
+if [[ "$1" == "--debug" ]]; then
+  args="-s ASSERTIONS=1 SAFE_HEAP=1 -O0"
+fi
+
+mkdir -p target/scratch target/release
+
+docker run                          \
+  --rm                              \
+  -v $(pwd):/src                    \
+  -u $(id -u)                       \
+  trzeci/emscripten-slim            \
+                                    \
+  emcc                              \
+  -s WASM=1                         \
+  -s ALLOW_MEMORY_GROWTH            \
+  -s MAIN_MODULE=1                  \
+  -s EXPORT_ALL=1                   \
+  $args                             \
+  -std=c99                          \
+  -D 'fprintf(...)='                \
+  -I lib/src                        \
+  -I lib/include                    \
+  -I lib/utf8proc                   \
+  --js-library lib/web/imports.js   \
+  --pre-js lib/web/prefix.js        \
+  --post-js lib/web/binding.js      \
+  lib/src/lib.c                     \
+  lib/web/binding.c                 \
+  -o target/scratch/tree-sitter.js
+
+if [ ! -d lib/web/node_modules/terser ]; then
+  (
+    cd lib/web
+    npm install
+  )
+fi
+
+lib/web/node_modules/.bin/terser   \
+  --compress                       \
+  --mangle                         \
+  --keep-fnames                    \
+  --keep-classnames                \
+  -- target/scratch/tree-sitter.js \
+  > target/release/tree-sitter.js
+
+mv target/scratch/tree-sitter.wasm target/release/tree-sitter.wasm
diff --git a/script/regenerate-fixtures b/script/generate-fixtures
similarity index 52%
rename from script/regenerate-fixtures
rename to script/generate-fixtures
index c47c53f9..6296d8ab 100755
--- a/script/regenerate-fixtures
+++ b/script/generate-fixtures
@@ -7,27 +7,16 @@ cargo build --release
 root_dir=$PWD
 tree_sitter=${root_dir}/target/release/tree-sitter
 grammars_dir=${root_dir}/test/fixtures/grammars
-
-grammar_names=(
-  bash
-  c
-  cpp
-  embedded-template
-  go
-  html
-  javascript
-  json
-  python
-  rust
-)
+grammar_names=$(ls $grammars_dir)
 
 if [[ "$#" > 0 ]]; then
   grammar_names=($1)
 fi
 
-for grammar_name in "${grammar_names[@]}"; do
+for grammar_name in $grammar_names; do
   echo "Regenerating ${grammar_name} parser"
-  cd ${grammars_dir}/${grammar_name}
-  $tree_sitter generate src/grammar.json
-  cd $PWD
+  (
+    cd ${grammars_dir}/${grammar_name}
+    $tree_sitter generate src/grammar.json
+  )
 done
diff --git a/script/generate-fixtures-wasm b/script/generate-fixtures-wasm
new file mode 100755
index 00000000..cbcf88bd
--- /dev/null
+++ b/script/generate-fixtures-wasm
@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+
+set -e
+
+cargo build --release
+
+root_dir=$PWD
+tree_sitter=${root_dir}/target/release/tree-sitter
+grammars_dir=${root_dir}/test/fixtures/grammars
+grammar_names=(
+  c
+  javascript
+  python
+)
+
+if [[ "$#" > 0 ]]; then
+  grammar_names=($1)
+fi
+
+for grammar_name in ${grammar_names[@]}; do
+  echo "Compiling ${grammar_name} parser to wasm"
+  $tree_sitter build-wasm ${grammars_dir}/${grammar_name}
+done
+
+mv tree-sitter-*.wasm target/release/
diff --git a/script/regenerate-fixtures.cmd b/script/generate-fixtures.cmd
similarity index 100%
rename from script/regenerate-fixtures.cmd
rename to script/generate-fixtures.cmd
diff --git a/script/serve-docs b/script/serve-docs
index b7776fd1..f3a80a15 100755
--- a/script/serve-docs
+++ b/script/serve-docs
@@ -1,4 +1,28 @@
 #!/bin/bash
 
+root=$PWD
 cd docs
-bundle exec jekyll serve "$@"
+
+bundle exec jekyll serve "$@" &
+
+bundle exec ruby <<RUBY &
+  require "listen"
+
+  def copy_wasm_files
+    `cp $root/target/release/*.{js,wasm} $root/docs/assets/js/`
+  end
+
+  puts "Copying WASM files to docs folder..."
+  copy_wasm_files
+
+  puts "Watching release directory"
+  listener = Listen.to("$root/target/release", only: /^tree-sitter\.(js|wasm)$/, wait_for_delay: 2) do
+    puts "WASM files updated. Copying new files to docs folder..."
+    copy_wasm_files
+  end
+
+  listener.start
+  sleep
+RUBY
+
+wait
diff --git a/script/test-wasm b/script/test-wasm
new file mode 100755
index 00000000..380ccab7
--- /dev/null
+++ b/script/test-wasm
@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+set -e
+
+cd lib/web
+
+if [ ! -d "node_modules/chai" ] || [ ! -d "node_modules/mocha" ]; then
+  echo "Installing test dependencies..."
+  npm install
+fi
+
+./node_modules/.bin/mocha