diff --git a/cli/npm/install.js b/cli/npm/install.js
index b008947c..c18ae6b5 100755
--- a/cli/npm/install.js
+++ b/cli/npm/install.js
@@ -40,7 +40,7 @@ const matrix = {
 
 // Determine the URL of the file.
 const platform = matrix.platform[process.platform];
-const arch = platform && platform.arch[process.arch];
+const arch = platform?.arch[process.arch];
 
 if (!platform || !platform.name || !arch || !arch.name) {
   console.error(
@@ -91,7 +91,7 @@ function get(url, callback) {
     }
   };
 
-  const proxyEnv = process.env['HTTPS_PROXY'] || process.env['https_proxy'];
+  const proxyEnv = process.env.HTTPS_PROXY || process.env.https_proxy;
   if (!proxyEnv) {
     https.get(url, processResponse);
     return;
diff --git a/cli/src/generate/dsl.js b/cli/src/generate/dsl.js
index 581aeddd..7c376c80 100644
--- a/cli/src/generate/dsl.js
+++ b/cli/src/generate/dsl.js
@@ -23,7 +23,7 @@ function alias(rule, value) {
       }
   }
 
-  throw new Error('Invalid alias value ' + value);
+  throw new Error(`Invalid alias value ${value}`);
 }
 
 function blank() {
@@ -35,7 +35,7 @@ function blank() {
 function field(name, rule) {
   return {
     type: "FIELD",
-    name: name,
+    name,
     content: normalize(rule)
   }
 }
@@ -156,7 +156,7 @@ function seq(...elements) {
 function sym(name) {
   return {
     type: "SYMBOL",
-    name: name
+    name
   };
 }
 
@@ -201,17 +201,17 @@ function normalize(value) {
       if (typeof value.type === 'string') {
         return value;
       } else {
-        throw new TypeError("Invalid rule: " + value.toString());
+        throw new TypeError(`Invalid rule: ${value}`);
       }
   }
 }
 
 function RuleBuilder(ruleMap) {
   return new Proxy({}, {
-    get(target, propertyName) {
+    get(_, propertyName) {
       const symbol = sym(propertyName);
 
-      if (!ruleMap || ruleMap.hasOwnProperty(propertyName)) {
+      if (!ruleMap || Object.prototype.hasOwnProperty.call(ruleMap, propertyName)) {
         return symbol;
       } else {
         const error = new ReferenceError(`Undefined symbol '${propertyName}'`);
@@ -256,10 +256,10 @@ function grammar(baseGrammar, options) {
   }
 
   const ruleMap = {};
-  for (const key in options.rules) {
+  for (const key of Object.keys(options.rules)) {
     ruleMap[key] = true;
   }
-  for (const key in baseGrammar.rules) {
+  for (const key of Object.keys(baseGrammar.rules)) {
     ruleMap[key] = true;
   }
   for (const external of externals) {
@@ -279,16 +279,16 @@ function grammar(baseGrammar, options) {
     throw new Error("Grammar's 'name' property must not start with a digit and cannot contain non-word characters.");
   }
 
-  let rules = Object.assign({}, baseGrammar.rules);
+  const rules = Object.assign({}, baseGrammar.rules);
   if (options.rules) {
     if (typeof options.rules !== "object") {
       throw new Error("Grammar's 'rules' property must be an object.");
     }
 
-    for (const ruleName in options.rules) {
+    for (const ruleName of Object.keys(options.rules)) {
       const ruleFn = options.rules[ruleName];
       if (typeof ruleFn !== "function") {
-        throw new Error("Grammar rules must all be functions. '" + ruleName + "' rule is not.");
+        throw new Error(`Grammar rules must all be functions. '${ruleName}' rule is not.`);
       }
       rules[ruleName] = normalize(ruleFn.call(ruleBuilder, ruleBuilder, baseGrammar.rules[ruleName]));
     }
@@ -403,7 +403,7 @@ function grammar(baseGrammar, options) {
     });
   }
 
-  if (Object.keys(rules).length == 0) {
+  if (Object.keys(rules).length === 0) {
     throw new Error("Grammar must have at least one rule.");
   }
 
diff --git a/docs/assets/js/playground.js b/docs/assets/js/playground.js
index 62bff362..5864d979 100644
--- a/docs/assets/js/playground.js
+++ b/docs/assets/js/playground.js
@@ -1,7 +1,7 @@
 let tree;
 
 (async () => {
-  const CAPTURE_REGEX = /@\s*([\w\._-]+)/g;
+  const CAPTURE_REGEX = /@\s*([\w._-]+)/g;
   const COLORS_BY_INDEX = [
     'blue',
     'chocolate',
@@ -18,8 +18,6 @@ let tree;
     'sienna',
   ];
 
-  const scriptURL = document.currentScript.getAttribute('src');
-
   const codeInput = document.getElementById('code-input');
   const languageSelect = document.getElementById('language-select');
   const loggingCheckbox = document.getElementById('logging-checkbox');
@@ -102,8 +100,8 @@ let tree;
     handleQueryChange();
   }
 
-  async function handleCodeChange(editor, changes) {
-    const newText = codeEditor.getValue() + '\n';
+  async function handleCodeChange(_editor, changes) {
+    const newText = `${codeEditor.getValue()}\n`;
     const edits = tree && changes && changes.map(treeEditForEditorChange);
 
     const start = performance.now();
@@ -128,9 +126,9 @@ let tree;
     isRendering++;
     const cursor = tree.walk();
 
-    let currentRenderCount = parseCount;
+    const currentRenderCount = parseCount;
     let row = '';
-    let rows = [];
+    const rows = [];
     let finishedRow = false;
     let visitedChildren = false;
     let indentLevel = 0;
@@ -319,7 +317,7 @@ let tree;
         start.column > end.column
       )
     ) {
-      let swap = end;
+      const swap = end;
       end = start;
       start = swap;
     }
@@ -445,14 +443,14 @@ let tree;
   }
 
   function debounce(func, wait, immediate) {
-    var timeout;
+    let timeout;
     return function() {
-      var context = this, args = arguments;
-      var later = function() {
+      const context = this, args = arguments;
+      const later = function() {
         timeout = null;
         if (!immediate) func.apply(context, args);
       };
-      var callNow = immediate && !timeout;
+      const callNow = immediate && !timeout;
       clearTimeout(timeout);
       timeout = setTimeout(later, wait);
       if (callNow) func.apply(context, args);
diff --git a/lib/binding_web/binding.js b/lib/binding_web/binding.js
index 295f13b2..2b4696c3 100644
--- a/lib/binding_web/binding.js
+++ b/lib/binding_web/binding.js
@@ -91,7 +91,7 @@ class ParserImpl {
 
     let rangeCount = 0;
     let rangeAddress = 0;
-    if (options && options.includedRanges) {
+    if (options?.includedRanges) {
       rangeCount = options.includedRanges.length;
       rangeAddress = C._calloc(rangeCount, SIZE_OF_RANGE);
       let address = rangeAddress;
@@ -349,6 +349,7 @@ class Node {
   childForFieldName(fieldName) {
     const fieldId = this.tree.language.fields.indexOf(fieldName);
     if (fieldId !== -1) return this.childForFieldId(fieldId);
+    return null;
   }
 
   fieldNameForChild(index) {
@@ -365,6 +366,7 @@ class Node {
   childrenForFieldName(fieldName) {
     const fieldId = this.tree.language.fields.indexOf(fieldName);
     if (fieldId !== -1 && fieldId !== 0) return this.childrenForFieldId(fieldId);
+    return [];
   }
 
   childrenForFieldId(fieldId) {
@@ -863,6 +865,7 @@ class Language {
   lookaheadIterator(stateId) {
     const address = C._ts_lookahead_iterator_new(this[0], stateId);
     if (address) return new LookaheadIterable(INTERNAL, address, this);
+    return null;
   }
 
   query(source) {
@@ -991,7 +994,7 @@ class Language {
               if (steps[2].type === 'capture') {
                 const captureName1 = steps[1].name;
                 const captureName2 = steps[2].name;
-                textPredicates[i].push(function(captures) {
+                textPredicates[i].push((captures) => {
                   const nodes1 = [];
                   const nodes2 = [];
                   for (const c of captures) {
@@ -1012,7 +1015,7 @@ class Language {
                 const stringValue = steps[2].value;
                 const matches = (n) => n.text === stringValue;
                 const doesNotMatch = (n) => n.text !== stringValue;
-                textPredicates[i].push(function(captures) {
+                textPredicates[i].push((captures) => {
                   const nodes = [];
                   for (const c of captures) {
                     if (c.name === captureName) nodes.push(c.node);
@@ -1048,7 +1051,7 @@ class Language {
               captureName = steps[1].name;
               const regex = new RegExp(steps[2].value);
               matchAll = !operator.startsWith('any-');
-              textPredicates[i].push(function(captures) {
+              textPredicates[i].push((captures) => {
                 const nodes = [];
                 for (const c of captures) {
                   if (c.name === captureName) nodes.push(c.node.text);
@@ -1119,7 +1122,7 @@ class Language {
               }
               captureName = steps[1].name;
               const values = steps.slice(2).map((s) => s.value);
-              textPredicates[i].push(function(captures) {
+              textPredicates[i].push((captures) => {
                 const nodes = [];
                 for (const c of captures) {
                   if (c.name === captureName) nodes.push(c.node.text);
@@ -1301,7 +1304,7 @@ class Query {
     const startAddress = getValue(TRANSFER_BUFFER + SIZE_OF_INT, 'i32');
     const didExceedMatchLimit = getValue(TRANSFER_BUFFER + 2 * SIZE_OF_INT, 'i32');
     const result = new Array(rawCount);
-    this.exceededMatchLimit = !!didExceedMatchLimit;
+    this.exceededMatchLimit = Boolean(didExceedMatchLimit);
 
     let filteredCount = 0;
     let address = startAddress;
@@ -1364,7 +1367,7 @@ class Query {
     const startAddress = getValue(TRANSFER_BUFFER + SIZE_OF_INT, 'i32');
     const didExceedMatchLimit = getValue(TRANSFER_BUFFER + 2 * SIZE_OF_INT, 'i32');
     const result = [];
-    this.exceededMatchLimit = !!didExceedMatchLimit;
+    this.exceededMatchLimit = Boolean(didExceedMatchLimit);
 
     const captures = [];
     let address = startAddress;
@@ -1490,15 +1493,15 @@ function unmarshalNode(tree, address = TRANSFER_BUFFER) {
 }
 
 function marshalTreeCursor(cursor, address = TRANSFER_BUFFER) {
-  setValue(address + 0 * SIZE_OF_INT, cursor[0], 'i32'),
-  setValue(address + 1 * SIZE_OF_INT, cursor[1], 'i32'),
+  setValue(address + 0 * SIZE_OF_INT, cursor[0], 'i32');
+  setValue(address + 1 * SIZE_OF_INT, cursor[1], 'i32');
   setValue(address + 2 * SIZE_OF_INT, cursor[2], 'i32');
   setValue(address + 3 * SIZE_OF_INT, cursor[3], 'i32');
 }
 
 function unmarshalTreeCursor(cursor) {
-  cursor[0] = getValue(TRANSFER_BUFFER + 0 * SIZE_OF_INT, 'i32'),
-  cursor[1] = getValue(TRANSFER_BUFFER + 1 * SIZE_OF_INT, 'i32'),
+  cursor[0] = getValue(TRANSFER_BUFFER + 0 * SIZE_OF_INT, 'i32');
+  cursor[1] = getValue(TRANSFER_BUFFER + 1 * SIZE_OF_INT, 'i32');
   cursor[2] = getValue(TRANSFER_BUFFER + 2 * SIZE_OF_INT, 'i32');
   cursor[3] = getValue(TRANSFER_BUFFER + 3 * SIZE_OF_INT, 'i32');
 }
diff --git a/lib/binding_web/imports.js b/lib/binding_web/imports.js
index b0d1d9f5..dfb65bbe 100644
--- a/lib/binding_web/imports.js
+++ b/lib/binding_web/imports.js
@@ -1,5 +1,5 @@
 mergeInto(LibraryManager.library, {
-  tree_sitter_parse_callback: function(
+  tree_sitter_parse_callback(
     inputBufferAddress,
     index,
     row,
@@ -7,7 +7,7 @@ mergeInto(LibraryManager.library, {
     lengthAddress,
   ) {
     const INPUT_BUFFER_SIZE = 10 * 1024;
-    const string = currentParseCallback(index, {row: row, column: column});
+    const string = currentParseCallback(index, {row, column});
     if (typeof string === 'string') {
       setValue(lengthAddress, string.length, 'i32');
       stringToUTF16(string, inputBufferAddress, INPUT_BUFFER_SIZE);
@@ -16,7 +16,7 @@ mergeInto(LibraryManager.library, {
     }
   },
 
-  tree_sitter_log_callback: function(isLexMessage, messageAddress) {
+  tree_sitter_log_callback(isLexMessage, messageAddress) {
     if (currentLogCallback) {
       const message = UTF8ToString(messageAddress);
       currentLogCallback(message, isLexMessage !== 0);
diff --git a/lib/binding_web/test/parser-test.js b/lib/binding_web/test/parser-test.js
index 4fa42c2b..4c58d020 100644
--- a/lib/binding_web/test/parser-test.js
+++ b/lib/binding_web/test/parser-test.js
@@ -251,7 +251,7 @@ describe('Parser', () => {
 
     it('handles long input strings', () => {
       const repeatCount = 10000;
-      const inputString = '[' + '0,'.repeat(repeatCount) + ']';
+      const inputString = `[${Array(repeatCount).fill('0').join(',')}]`;
 
       tree = parser.parse(inputString);
       assert.equal(tree.rootNode.type, 'program');
diff --git a/lib/binding_web/test/tree-test.js b/lib/binding_web/test/tree-test.js
index a190c982..c9216eb1 100644
--- a/lib/binding_web/test/tree-test.js
+++ b/lib/binding_web/test/tree-test.js
@@ -244,62 +244,47 @@ describe('Tree', () => {
         endIndex: 13,
       });
 
-      {
-        const copy = tree.walk();
-        copy.resetTo(cursor);
+      const copy = tree.walk();
+      copy.resetTo(cursor);
 
-        assert(copy.gotoPreviousSibling());
-        assertCursorState(copy, {
-          nodeType: '+',
-          nodeIsNamed: false,
-          startPosition: {row: 0, column: 6},
-          endPosition: {row: 0, column: 7},
-          startIndex: 6,
-          endIndex: 7,
-        });
+      assert(copy.gotoPreviousSibling());
+      assertCursorState(copy, {
+        nodeType: '+',
+        nodeIsNamed: false,
+        startPosition: {row: 0, column: 6},
+        endPosition: {row: 0, column: 7},
+        startIndex: 6,
+        endIndex: 7,
+      });
 
-        assert(copy.gotoPreviousSibling());
-        assertCursorState(copy, {
-          nodeType: 'binary_expression',
-          nodeIsNamed: true,
-          startPosition: {row: 0, column: 0},
-          endPosition: {row: 0, column: 5},
-          startIndex: 0,
-          endIndex: 5,
-        });
+      assert(copy.gotoPreviousSibling());
+      assertCursorState(copy, {
+        nodeType: 'binary_expression',
+        nodeIsNamed: true,
+        startPosition: {row: 0, column: 0},
+        endPosition: {row: 0, column: 5},
+        startIndex: 0,
+        endIndex: 5,
+      });
 
-        assert(copy.gotoLastChild());
-        assertCursorState(copy, {
-          nodeType: 'identifier',
-          nodeIsNamed: true,
-          startPosition: {row: 0, column: 4},
-          endPosition: {row: 0, column: 5},
-          startIndex: 4,
-          endIndex: 5,
-        });
+      assert(copy.gotoLastChild());
+      assertCursorState(copy, {
+        nodeType: 'identifier',
+        nodeIsNamed: true,
+        startPosition: {row: 0, column: 4},
+        endPosition: {row: 0, column: 5},
+        startIndex: 4,
+        endIndex: 5,
+      });
 
-        assert(copy.gotoParent());
-        assert(copy.gotoParent());
-        assert.equal(copy.nodeType, 'binary_expression');
-        assert(copy.gotoParent());
-        assert.equal(copy.nodeType, 'expression_statement');
-        assert(copy.gotoParent());
-        assert.equal(copy.nodeType, 'program');
-        assert(!copy.gotoParent());
-      }
-
-      // const childIndex = cursor.gotoFirstChildForIndex(12);
-      // assertCursorState(cursor, {
-      //   nodeType: 'identifier',
-      //   nodeIsNamed: true,
-      //   startPosition: {row: 0, column: 12},
-      //   endPosition: {row: 0, column: 13},
-      //   startIndex: 12,
-      //   endIndex: 13
-      // });
-      // assert.equal(childIndex, 2);
-      // assert(!cursor.gotoNextSibling());
-      // assert(cursor.gotoParent());
+      assert(copy.gotoParent());
+      assert(copy.gotoParent());
+      assert.equal(copy.nodeType, 'binary_expression');
+      assert(copy.gotoParent());
+      assert.equal(copy.nodeType, 'expression_statement');
+      assert(copy.gotoParent());
+      assert.equal(copy.nodeType, 'program');
+      assert(!copy.gotoParent());
 
       assert(cursor.gotoParent());
       assert.equal(cursor.nodeType, 'binary_expression');
@@ -414,7 +399,7 @@ function spliceInput(input, startIndex, lengthRemoved, newText) {
 function getExtent(text) {
   let row = 0;
   let index;
-  for (index = 0; index != -1; index = text.indexOf('\n', index)) {
+  for (index = 0; index !== -1; index = text.indexOf('\n', index)) {
     index++;
     row++;
   }