chore: lint usage of Arrays (jestjs#14804)

.eslintrc.cjs

@@ -662,6 +662,12 @@ module.exports = {
     // enforced by `@typescript-eslint/no-this-alias` already
     'unicorn/no-this-assignment': 'off',
 
+    // Not an issue with TypeScript
+    'unicorn/no-array-callback-reference': 'off',
+
+    // reduce is fine
+    'unicorn/no-array-reduce': 'off',
+
     // nah
     'unicorn/consistent-destructuring': 'off',
     'unicorn/no-nested-ternary': 'off',
@@ -676,35 +682,24 @@ module.exports = {
 
     // TODO: decide whether or not we want these
     'unicorn/filename-case': 'off',
-    'unicorn/no-array-callback-reference': 'off',
-    'unicorn/no-array-reduce': 'off',
     'unicorn/prefer-reflect-apply': 'off',
 
     // TODO: turn on at some point
     'unicorn/catch-error-name': 'off',
     'unicorn/consistent-function-scoping': 'off',
     'unicorn/error-message': 'off',
     'unicorn/escape-case': 'off',
-    'unicorn/no-array-method-this-argument': 'off',
-    'unicorn/no-array-push-push': 'off',
     'unicorn/no-await-expression-member': 'off',
     'unicorn/no-console-spaces': 'off',
     'unicorn/no-empty-file': 'off',
     'unicorn/no-for-loop': 'off',
     'unicorn/no-hex-escape': 'off',
-    'unicorn/no-instanceof-array': 'off',
-    'unicorn/no-new-array': 'off',
     'unicorn/no-object-as-default-parameter': 'off',
     'unicorn/no-thenable': 'off',
     'unicorn/no-typeof-undefined': 'off',
     'unicorn/no-useless-promise-resolve-reject': 'off',
     'unicorn/no-useless-undefined': 'off',
     'unicorn/number-literal-case': 'off',
-    'unicorn/prefer-array-flat': 'off',
-    'unicorn/prefer-array-flat-map': 'off',
-    'unicorn/prefer-array-index-of': 'off',
-    'unicorn/prefer-array-some': 'off',
-    'unicorn/prefer-at': 'off',
     'unicorn/prefer-date-now': 'off',
     'unicorn/prefer-logical-operator-over-ternary': 'off',
     'unicorn/prefer-math-trunc': 'off',

e2e/Utils.ts

@@ -267,7 +267,7 @@ const sortTests = (stdout: string) =>
       if (['RUNS', 'PASS', 'FAIL'].includes(line.slice(0, 4))) {
         tests.push([line]);
       } else {
-        tests[tests.length - 1].push(line);
+        tests.at(-1)!.push(line);
       }
       return tests;
     }, [])

e2e/babel-plugin-jest-hoist/__tests__/integration.test.js

@@ -44,7 +44,7 @@ jest.mock('../__test_modules__/f', () => {
     fn: () => {
       // The `jest.mock` transform will allow require, built-ins and globals.
       const path = require('path');
-      const array = new Array(3);
+      const array = Array.from({length: 3});
       array[0] = path.sep;
       return jest.fn(() => array);
     },

packages/expect-utils/src/utils.ts

@@ -334,7 +334,7 @@ const isObject = (a: any) => a !== null && typeof a === 'object';
 const isObjectWithKeys = (a: any) =>
   isObject(a) &&
   !(a instanceof Error) &&
-  !(a instanceof Array) &&
+  !Array.isArray(a) &&
   !(a instanceof Date);
 
 export const subsetEquality = (

packages/jest-circus/src/__tests__/shuffleArray.test.ts

@@ -12,7 +12,7 @@ describe('rngBuilder', () => {
   // Some people will be using seeds relying on a particular order
   test.each([1, 2, 4, 8, 16])('creates a randomizer given seed %s', seed => {
     const rng = rngBuilder(seed);
-    const results = new Array(10).fill(0).map(() => rng.next(0, 10));
+    const results = Array.from({length: 10}).map(() => rng.next(0, 10));
     expect(results).toMatchSnapshot();
   });
 });

packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapterInit.ts

@@ -198,7 +198,7 @@ export const runAndTransformResultsToJestFormat = async ({
         retryReasons: testResult.retryReasons,
         startAt: testResult.startedAt,
         status,
-        title: testResult.testPath[testResult.testPath.length - 1],
+        title: testResult.testPath.at(-1)!,
       };
     },
   );

packages/jest-circus/src/utils.ts

@@ -401,8 +401,7 @@ const makeTestResults = (
       const child = currentBlock.children[i];
 
       if (child.type === 'describeBlock') {
-        stack.push([currentBlock, i + 1]);
-        stack.push([child, 0]);
+        stack.push([currentBlock, i + 1], [child, 0]);
         break;
       }
       if (child.type === 'test') {
@@ -478,7 +477,7 @@ const resolveTestCaseStartInfo = (
     name => name !== ROOT_DESCRIBE_BLOCK_NAME,
   );
   const fullName = ancestorTitles.join(' ');
-  const title = testNamesPath[testNamesPath.length - 1];
+  const title = testNamesPath.at(-1)!;
   // remove title
   ancestorTitles.pop();
   return {

packages/jest-config/src/__tests__/resolveConfigPath.test.ts

@@ -182,11 +182,9 @@ describe.each(JEST_CONFIG_EXT_ORDER.slice(0))(
 );
 
 const pickPairsWithSameOrder = <T>(array: ReadonlyArray<T>) =>
-  array
-    .map((value1, idx, arr) =>
-      arr.slice(idx + 1).map(value2 => [value1, value2]),
-    )
-    .flat();
+  array.flatMap((value1, idx, arr) =>
+    arr.slice(idx + 1).map(value2 => [value1, value2]),
+  );
 
 test('pickPairsWithSameOrder', () => {
   expect(pickPairsWithSameOrder([1, 2, 3])).toStrictEqual([

packages/jest-config/src/index.ts

@@ -231,9 +231,9 @@ const ensureNoDuplicateConfigs = (
         String(configPath),
       )}:
 
-  Project 1: ${chalk.bold(projects[parsedConfigs.findIndex(x => x === config)])}
+  Project 1: ${chalk.bold(projects[parsedConfigs.indexOf(config)])}
   Project 2: ${chalk.bold(
-    projects[parsedConfigs.findIndex(x => x === configPathMap.get(configPath))],
+    projects[parsedConfigs.indexOf(configPathMap.get(configPath))],
   )}
 
 This usually means that your ${chalk.bold(

packages/jest-core/src/__tests__/testSchedulerHelper.test.js

@@ -23,26 +23,26 @@ const getTestMock = () => ({
 const getTestsMock = () => [getTestMock(), getTestMock()];
 
 test.each`
-  tests              | timings        | detectOpenHandles | runInBand | maxWorkers   | watch    | workerIdleMemoryLimit | expectedResult
-  ${[getTestMock()]} | ${[500, 500]}  | ${false}          | ${false}  | ${undefined} | ${true}  | ${undefined}          | ${false}
-  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${false}  | ${1}         | ${true}  | ${undefined}          | ${false}
-  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${false}  | ${2}         | ${true}  | ${undefined}          | ${false}
-  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${true}   | ${1}         | ${true}  | ${undefined}          | ${true}
-  ${[getTestMock()]} | ${[2000, 500]} | ${false}          | ${false}  | ${undefined} | ${true}  | ${undefined}          | ${false}
-  ${getTestMock()}   | ${[500, 500]}  | ${false}          | ${false}  | ${undefined} | ${true}  | ${undefined}          | ${false}
-  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${false}  | ${1}         | ${false} | ${undefined}          | ${true}
-  ${getTestMock()}   | ${[2000, 500]} | ${false}          | ${false}  | ${2}         | ${false} | ${undefined}          | ${false}
-  ${[getTestMock()]} | ${[2000]}      | ${false}          | ${false}  | ${undefined} | ${false} | ${undefined}          | ${true}
-  ${getTestsMock()}  | ${[500, 500]}  | ${false}          | ${false}  | ${undefined} | ${false} | ${undefined}          | ${true}
-  ${new Array(45)}   | ${[500]}       | ${false}          | ${false}  | ${undefined} | ${false} | ${undefined}          | ${false}
-  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${false}  | ${undefined} | ${false} | ${undefined}          | ${false}
-  ${getTestsMock()}  | ${[2000, 500]} | ${true}           | ${false}  | ${undefined} | ${false} | ${undefined}          | ${true}
-  ${[getTestMock()]} | ${[500, 500]}  | ${false}          | ${false}  | ${undefined} | ${true}  | ${'500MB'}            | ${false}
-  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${false}  | ${1}         | ${true}  | ${'500MB'}            | ${false}
-  ${getTestsMock()}  | ${[2000, 500]} | ${false}          | ${false}  | ${1}         | ${false} | ${'500MB'}            | ${false}
-  ${[getTestMock()]} | ${[2000]}      | ${false}          | ${false}  | ${undefined} | ${false} | ${'500MB'}            | ${false}
-  ${getTestsMock()}  | ${[500, 500]}  | ${false}          | ${false}  | ${undefined} | ${false} | ${'500MB'}            | ${false}
-  ${getTestsMock()}  | ${[2000, 500]} | ${true}           | ${false}  | ${undefined} | ${false} | ${'500MB'}            | ${true}
+  tests                       | timings        | detectOpenHandles | runInBand | maxWorkers   | watch    | workerIdleMemoryLimit | expectedResult
+  ${[getTestMock()]}          | ${[500, 500]}  | ${false}          | ${false}  | ${undefined} | ${true}  | ${undefined}          | ${false}
+  ${getTestsMock()}           | ${[2000, 500]} | ${false}          | ${false}  | ${1}         | ${true}  | ${undefined}          | ${false}
+  ${getTestsMock()}           | ${[2000, 500]} | ${false}          | ${false}  | ${2}         | ${true}  | ${undefined}          | ${false}
+  ${getTestsMock()}           | ${[2000, 500]} | ${false}          | ${true}   | ${1}         | ${true}  | ${undefined}          | ${true}
+  ${[getTestMock()]}          | ${[2000, 500]} | ${false}          | ${false}  | ${undefined} | ${true}  | ${undefined}          | ${false}
+  ${getTestMock()}            | ${[500, 500]}  | ${false}          | ${false}  | ${undefined} | ${true}  | ${undefined}          | ${false}
+  ${getTestsMock()}           | ${[2000, 500]} | ${false}          | ${false}  | ${1}         | ${false} | ${undefined}          | ${true}
+  ${getTestMock()}            | ${[2000, 500]} | ${false}          | ${false}  | ${2}         | ${false} | ${undefined}          | ${false}
+  ${[getTestMock()]}          | ${[2000]}      | ${false}          | ${false}  | ${undefined} | ${false} | ${undefined}          | ${true}
+  ${getTestsMock()}           | ${[500, 500]}  | ${false}          | ${false}  | ${undefined} | ${false} | ${undefined}          | ${true}
+  ${Array.from({length: 45})} | ${[500]}       | ${false}          | ${false}  | ${undefined} | ${false} | ${undefined}          | ${false}
+  ${getTestsMock()}           | ${[2000, 500]} | ${false}          | ${false}  | ${undefined} | ${false} | ${undefined}          | ${false}
+  ${getTestsMock()}           | ${[2000, 500]} | ${true}           | ${false}  | ${undefined} | ${false} | ${undefined}          | ${true}
+  ${[getTestMock()]}          | ${[500, 500]}  | ${false}          | ${false}  | ${undefined} | ${true}  | ${'500MB'}            | ${false}
+  ${getTestsMock()}           | ${[2000, 500]} | ${false}          | ${false}  | ${1}         | ${true}  | ${'500MB'}            | ${false}
+  ${getTestsMock()}           | ${[2000, 500]} | ${false}          | ${false}  | ${1}         | ${false} | ${'500MB'}            | ${false}
+  ${[getTestMock()]}          | ${[2000]}      | ${false}          | ${false}  | ${undefined} | ${false} | ${'500MB'}            | ${false}
+  ${getTestsMock()}           | ${[500, 500]}  | ${false}          | ${false}  | ${undefined} | ${false} | ${'500MB'}            | ${false}
+  ${getTestsMock()}           | ${[2000, 500]} | ${true}           | ${false}  | ${undefined} | ${false} | ${'500MB'}            | ${true}
 `(
   'shouldRunInBand() - should return $expectedResult for runInBand mode',
   ({

packages/jest-core/src/__tests__/watch.test.js

@@ -720,7 +720,7 @@ describe('Watch mode flows', () => {
 
       // We need the penultimate call as Jest forces a final call to restore
       // updateSnapshot because it's not sticky after a run…?
-      const lastCall = updateGlobalConfig.mock.calls.slice(-2)[0];
+      const lastCall = updateGlobalConfig.mock.calls.at(-2);
       // eslint-disable-next-line jest/valid-expect
       let expector = expect(lastCall[1]);
       if (!ok) {

packages/jest-core/src/cli/index.ts

@@ -145,7 +145,9 @@ const buildContextsAndHasteMaps = async (
   globalConfig: Config.GlobalConfig,
   outputStream: WriteStream,
 ) => {
-  const hasteMapInstances = new Array(configs.length);
+  const hasteMapInstances = Array.from<IHasteMap>({
+    length: configs.length,
+  });
   const contexts = await Promise.all(
     configs.map(async (config, index) => {
       createDirectory(config.cacheDirectory);

packages/jest-core/src/runJest.ts

@@ -284,7 +284,7 @@ export default async function runJest({
             );
           }),
         )
-      ).reduce((total, paths) => total.concat(paths), []);
+      ).flat();
       testSchedulerContext.sourcesRelatedToTestsInChangedFiles = new Set(
         sourcesRelatedToTestsInChangedFilesArray,
       );

packages/jest-fake-timers/src/legacyFakeTimers.ts

@@ -513,7 +513,7 @@ export default class FakeTimers<TimerRef = unknown> {
 
     this._timerAPIs.setImmediate(() => {
       if (!this._disposed) {
-        if (this._immediates.find(x => x.uuid === uuid)) {
+        if (this._immediates.some(x => x.uuid === uuid)) {
           try {
             callback.apply(null, args);
           } finally {

packages/jest-haste-map/src/crawlers/node.ts

@@ -151,8 +151,7 @@ function findNative(
     if (index) {
       args.push('-o');
     }
-    args.push('-iname');
-    args.push(`*.${ext}`);
+    args.push('-iname', `*.${ext}`);
   }
   if (extensions.length > 0) {
     args.push(')');

packages/jest-haste-map/src/index.ts

@@ -901,7 +901,7 @@ class HasteMap extends EventEmitter implements IHasteMap {
         .then(() => {
           // If we get duplicate events for the same file, ignore them.
           if (
-            eventsQueue.find(
+            eventsQueue.some(
               event =>
                 event.type === type &&
                 event.filePath === filePath &&

packages/jest-haste-map/src/watchers/NodeWatcher.js

@@ -219,7 +219,7 @@ module.exports = class NodeWatcher extends EventEmitter {
     let closest = {mtime: 0};
     let c = 0;
     // eslint-disable-next-line unicorn/no-array-for-each
-    Object.keys(this.dirRegistery[dir]).forEach(function (file, i, arr) {
+    Object.keys(this.dirRegistery[dir]).forEach((file, i, arr) => {
       fs.lstat(path.join(dir, file), (error, stat) => {
         if (found) {
           return;
@@ -242,7 +242,7 @@ module.exports = class NodeWatcher extends EventEmitter {
           }
         }
       });
-    }, this);
+    });
   }
 
   /**

packages/jest-haste-map/src/watchers/common.js

@@ -62,7 +62,8 @@ exports.isFileIncluded = function (globs, dot, doIgnore, relativePath) {
   }
   return globs.length > 0
     ? micromatch.some(relativePath, globs, {dot})
-    : dot || micromatch.some(relativePath, '**/*');
+    : // eslint-disable-next-line unicorn/no-array-method-this-argument
+      dot || micromatch.some(relativePath, '**/*');
 };
 
 /**

packages/jest-jasmine2/src/jasmine/CallTracker.ts

@@ -84,7 +84,7 @@ class CallTracker {
     };
 
     this.mostRecent = function () {
-      return calls[calls.length - 1];
+      return calls.at(-1)!;
     };
 
     this.reset = function () {

packages/jest-jasmine2/src/jasmine/Env.ts

@@ -147,7 +147,7 @@ export default function jasmineEnv(j$: Jasmine) {
       let currentDeclarationSuite = topSuite;
 
       const currentSuite = function () {
-        return currentlyExecutingSuites[currentlyExecutingSuites.length - 1];
+        return currentlyExecutingSuites.at(-1)!;
       };
 
       const currentRunnable = function () {

packages/jest-matcher-utils/src/__tests__/index.test.ts

@@ -101,7 +101,7 @@ describe('stringify()', () => {
   test('reduces maxWidth if stringifying very large arrays', () => {
     const big: any = [];
     const small: any = [];
-    const testString = new Array(1000).join('x');
+    const testString = Array.from({length: 1000}).join('x');
 
     for (let i = 0; i < 100; i += 1) {
       big[i] = testString;

packages/jest-mock/src/index.ts

@@ -566,7 +566,7 @@ export class ModuleMocker {
       this._mockState.set(f, state);
     }
     if (state.calls.length > 0) {
-      state.lastCall = state.calls[state.calls.length - 1];
+      state.lastCall = state.calls.at(-1);
     }
     return state;
   }

packages/jest-reporters/src/GitHubActionsReporter.ts

@@ -258,7 +258,7 @@ export default class GitHubActionsReporter extends BaseReporter {
   ): ResultTreeNode {
     const node: ResultTreeNode = {
       children: [],
-      name: ancestors[ancestors.length - 1],
+      name: ancestors.at(-1)!,
       passed: true,
     };
     const branches: Array<Array<string>> = [];

packages/jest-reporters/src/SummaryReporter.ts

@@ -105,7 +105,7 @@ export default class SummaryReporter extends BaseReporter {
   ): void {
     const {numTotalTestSuites, testResults, wasInterrupted} = aggregatedResults;
     if (numTotalTestSuites) {
-      const lastResult = testResults[testResults.length - 1];
+      const lastResult = testResults.at(-1);
       // Print a newline if the last test did not fail to line up newlines
       // similar to when an error would have been thrown in the test.
       if (

packages/jest-reporters/src/__tests__/SummaryReporter.test.js

@@ -53,7 +53,7 @@ test('snapshots needs update with npm test', () => {
       unmatched: 2,
     },
     startTime: 0,
-    testResults: {},
+    testResults: [],
   };
 
   process.env.npm_config_user_agent = 'npm';
@@ -78,7 +78,7 @@ test('snapshots needs update with yarn test', () => {
       unmatched: 2,
     },
     startTime: 0,
-    testResults: {},
+    testResults: [],
   };
 
   process.env.npm_config_user_agent = 'yarn';
@@ -116,7 +116,7 @@ test('snapshots all have results (no update)', () => {
       updated: 1,
     },
     startTime: 0,
-    testResults: {},
+    testResults: [],
   };
 
   requireReporter();
@@ -153,7 +153,7 @@ test('snapshots all have results (after update)', () => {
       updated: 1,
     },
     startTime: 0,
-    testResults: {},
+    testResults: [],
   };
 
   requireReporter();

packages/jest-resolve/src/__tests__/resolve.test.ts

@@ -740,7 +740,7 @@ describe('nodeModulesPaths', () => {
   it('provides custom module paths after node_modules', () => {
     const src = require.resolve('../');
     const result = nodeModulesPaths(src, {paths: ['./customFolder']});
-    expect(result[result.length - 1]).toBe('./customFolder');
+    expect(result.at(-1)).toBe('./customFolder');
   });
 
   it('provides custom module multy paths after node_modules', () => {

packages/jest-resolve/src/nodeModulesPaths.ts

@@ -47,7 +47,7 @@ export default function nodeModulesPaths(
 
   const paths: Array<string> = [physicalBasedir];
   let parsed = path.parse(physicalBasedir);
-  while (parsed.dir !== paths[paths.length - 1]) {
+  while (parsed.dir !== paths.at(-1)) {
     paths.push(parsed.dir);
     parsed = path.parse(parsed.dir);
   }

packages/jest-resolve/src/resolver.ts

@@ -518,7 +518,7 @@ export default class Resolver {
 
     const moduleDirectory = this._options.moduleDirectories;
     const paths = nodeModulesPaths(from, {moduleDirectory});
-    if (paths[paths.length - 1] === undefined) {
+    if (paths.at(-1) === undefined) {
       // circumvent node-resolve bug that adds `undefined` as last item.
       paths.pop();
     }

packages/jest-runtime/src/__tests__/runtime_require_module.test.js

@@ -136,7 +136,7 @@ describe('Runtime requireModule', () => {
     expect(exports.paths.length).toBeGreaterThan(0);
     const root = path.parse(process.cwd()).root;
     const globalPath = path.join(root, 'node_modules');
-    const rootIndex = exports.paths.findIndex(path => path === globalPath);
+    const rootIndex = exports.paths.indexOf(globalPath);
     for (const [index, path] of exports.paths.entries()) {
       if (index <= rootIndex) {
         expect(moduleDirectories.some(dir => path.endsWith(dir))).toBe(true);