ESLint 9

package.json

@@ -16,12 +16,13 @@
   ],
   "devDependencies": {
     "@release-it/conventional-changelog": "8.0.1",
+    "@types/eslint": "^8.56.10",
     "@types/jest": "27.0.2",
     "@types/node": "16.11.7",
     "@typescript-eslint/eslint-plugin": "5.3.1",
     "@typescript-eslint/parser": "5.3.1",
     "auto-changelog": "2.4.0",
-    "eslint": "8.57.0",
+    "eslint": "^9.0.0",
     "jest": "27.3.1",
     "prettier": "2.4.1",
     "release-it": "17.0.1",

src/prefer-arrow-functions.spec.ts

@@ -7,6 +7,9 @@ import {
 } from './config';
 import rule from './prefer-arrow-functions';
 
+// TODO: Remove this once Jest starts supporting modern JavaScript
+globalThis.structuredClone ??= obj => JSON.parse(JSON.stringify(obj));
+
 const alwaysValid = [
   {
     code: 'var foo = (bar) => bar;',
@@ -492,14 +495,6 @@ const invalidAndHasBlockStatement = [
     code: 'async function foo(a) { console.log(3); }',
     output: 'const foo = async (a) => { console.log(3); };',
   },
-  {
-    code: 'function foo(a) { console.log(3); }',
-    output: 'const foo = (a) => { console.log(3); };',
-  },
-  {
-    code: 'async function foo(a) { console.log(3); }',
-    output: 'const foo = async (a) => { console.log(3); };',
-  },
 
   // https://github.com/JamieMason/eslint-plugin-prefer-arrow-functions/issues/28
   {
@@ -576,22 +571,6 @@ const invalidAndHasBlockStatement = [
     code: 'var foo = async function() { console.log({a: false}); }',
     output: 'var foo = async () => { console.log({a: false}); }',
   },
-  {
-    code: 'var foo = function() { console.log({a: false}); }',
-    output: 'var foo = () => { console.log({a: false}); }',
-  },
-  {
-    code: 'var foo = async function() { console.log({a: false}); }',
-    output: 'var foo = async () => { console.log({a: false}); }',
-  },
-  {
-    code: 'function foo(a) { console.log({a: false}); }',
-    output: 'const foo = (a) => { console.log({a: false}); };',
-  },
-  {
-    code: 'async function foo(a) { console.log({a: false}); }',
-    output: 'const foo = async (a) => { console.log({a: false}); };',
-  },
   {
     code: 'function foo(a) { console.log({a: false}); }',
     output: 'const foo = (a) => { console.log({a: false}); };',
@@ -614,22 +593,6 @@ const invalidAndHasBlockStatement = [
     code: 'var foo = async function() {\n  console.log("World");\n}',
     output: 'var foo = async () => {\n  console.log("World");\n}',
   },
-  {
-    code: 'var foo = function() {\n  console.log("World");\n}',
-    output: 'var foo = () => {\n  console.log("World");\n}',
-  },
-  {
-    code: 'var foo = async function() {\n  console.log("World");\n}',
-    output: 'var foo = async () => {\n  console.log("World");\n}',
-  },
-  {
-    code: 'function foo(a) {\n  console.log(3);\n}',
-    output: 'const foo = (a) => {\n  console.log(3);\n};',
-  },
-  {
-    code: 'async function foo(a) {\n  console.log(3);\n}',
-    output: 'const foo = async (a) => {\n  console.log(3);\n};',
-  },
   {
     code: 'function foo(a) {\n  console.log(3);\n}',
     output: 'const foo = (a) => {\n  console.log(3);\n};',
@@ -750,7 +713,6 @@ const validWhenAllowNamedFunctions = [
   {
     // Make sure "allowNamedFunctions" works with typescript
     code: '() => { function foo(a: string): string { return `bar ${a}`;} }',
-    parser: require.resolve('@typescript-eslint/parser'),
   },
 ];
 
@@ -768,10 +730,6 @@ const invalidWhenAllowNamedFunctions = [
     code: '() => { var foo = function() { return () => "bar"; }; }',
     output: '() => { var foo = () => () => "bar"; }',
   },
-  {
-    code: '() => { var foo = function() { return "bar"; }; }',
-    output: '() => { var foo = () => "bar"; }',
-  },
   {
     code: 'module.exports = () => { var foo = function() { return "bar"; }; }',
     output: 'module.exports = () => { var foo = () => "bar"; }',
@@ -809,16 +767,15 @@ const invalidWhenAllowNamedFunctions = [
     output: `function foo(a: string): () => string {
       return () => \`bar \${a}\`;
     }`,
-    parser: require.resolve('@typescript-eslint/parser'),
   },
 ];
 
 const ruleTester = new RuleTester({
-  parser: require.resolve('@typescript-eslint/parser'),
-  parserOptions: {
-    ecmaFeatures: { jsx: false },
-    ecmaVersion: 8,
-    sourceType: 'module',
+  // TODO: Remove this `languageOptions` once the tests are updated for flat config:
+  languageOptions: {
+    ecmaVersion: 5, // Original value was 8 here
+    parser: require('@typescript-eslint/parser'),
+    sourceType: 'script' // Original value was 'module' here
   },
 });
 

src/prefer-arrow-functions.ts

@@ -43,7 +43,7 @@ export default {
     const classPropertiesAllowed = getOption('classPropertiesAllowed');
     const disallowPrototype = getOption('disallowPrototype');
     const returnStyle = getOption('returnStyle');
-    const sourceCode = context.getSourceCode();
+    const { sourceCode } = context;
 
     const isBlockStatementWithSingleReturn = (node) => {
       return (
@@ -193,8 +193,8 @@ export default {
     };
 
     const isPrototypeAssignment = (node) => {
-      return context
-        .getAncestors()
+      return sourceCode
+        .getAncestors(node)
         .reverse()
         .some((ancestor) => {
           const isPropertyOfReplacementPrototypeObject =
@@ -216,8 +216,8 @@ export default {
     };
 
     const isWithinClassBody = (node) => {
-      return context
-        .getAncestors()
+      return sourceCode
+        .getAncestors(node)
         .reverse()
         .some((ancestor) => {
           return ancestor.type === 'ClassBody';
@@ -334,4 +334,4 @@ export default {
       },
     };
   },
-};
+} as const;