chore: avoid using anonymous default exports

.eslintrc.js

@@ -185,6 +185,18 @@ module.exports = {
       files: 'packages/**/*.ts',
       rules: {
         '@typescript-eslint/explicit-module-boundary-types': 'error',
+        'import/no-anonymous-default-export': [
+          'error',
+          {
+            allowAnonymousClass: false,
+            allowAnonymousFunction: false,
+            allowArray: false,
+            allowArrowFunction: false,
+            allowCallExpression: false,
+            allowLiteral: false,
+            allowObject: true,
+          },
+        ],
       },
     },
     {

CHANGELOG.md

@@ -10,6 +10,8 @@
 
 ### Chore & Maintenance
 
+- `[*]` Avoid anonymous default exports ([#12313](https://github.com/facebook/jest/pull/12313))
+
 ### Performance
 
 ## 27.5.0

packages/babel-plugin-jest-hoist/src/index.ts

@@ -268,102 +268,106 @@ const extractJestObjExprIfHoistable = <T extends Node>(
 };
 
 /* eslint-disable sort-keys */
-export default (): PluginObj<{
+export default function jestHoist(): PluginObj<{
   declareJestObjGetterIdentifier: () => Identifier;
   jestObjGetterIdentifier?: Identifier;
-}> => ({
-  pre({path: program}) {
-    this.declareJestObjGetterIdentifier = () => {
-      if (this.jestObjGetterIdentifier) {
-        return this.jestObjGetterIdentifier;
-      }
+}> {
+  return {
+    pre({path: program}) {
+      this.declareJestObjGetterIdentifier = () => {
+        if (this.jestObjGetterIdentifier) {
+          return this.jestObjGetterIdentifier;
+        }
 
-      this.jestObjGetterIdentifier =
-        program.scope.generateUidIdentifier('getJestObj');
+        this.jestObjGetterIdentifier =
+          program.scope.generateUidIdentifier('getJestObj');
 
-      program.unshiftContainer('body', [
-        createJestObjectGetter({
-          GETTER_NAME: this.jestObjGetterIdentifier.name,
-          JEST_GLOBALS_MODULE_JEST_EXPORT_NAME,
-          JEST_GLOBALS_MODULE_NAME,
-        }),
-      ]);
+        program.unshiftContainer('body', [
+          createJestObjectGetter({
+            GETTER_NAME: this.jestObjGetterIdentifier.name,
+            JEST_GLOBALS_MODULE_JEST_EXPORT_NAME,
+            JEST_GLOBALS_MODULE_NAME,
+          }),
+        ]);
 
-      return this.jestObjGetterIdentifier;
-    };
-  },
-  visitor: {
-    ExpressionStatement(exprStmt) {
-      const jestObjExpr = extractJestObjExprIfHoistable(
-        exprStmt.get('expression'),
-      );
-      if (jestObjExpr) {
-        jestObjExpr.replaceWith(
-          callExpression(this.declareJestObjGetterIdentifier(), []),
+        return this.jestObjGetterIdentifier;
+      };
+    },
+    visitor: {
+      ExpressionStatement(exprStmt) {
+        const jestObjExpr = extractJestObjExprIfHoistable(
+          exprStmt.get('expression'),
         );
-      }
+        if (jestObjExpr) {
+          jestObjExpr.replaceWith(
+            callExpression(this.declareJestObjGetterIdentifier(), []),
+          );
+        }
+      },
     },
-  },
-  // in `post` to make sure we come after an import transform and can unshift above the `require`s
-  post({path: program}) {
-    const self = this;
-
-    visitBlock(program);
-    program.traverse({BlockStatement: visitBlock});
-
-    function visitBlock(block: NodePath<BlockStatement> | NodePath<Program>) {
-      // use a temporary empty statement instead of the real first statement, which may itself be hoisted
-      const [varsHoistPoint, callsHoistPoint] = block.unshiftContainer('body', [
-        emptyStatement(),
-        emptyStatement(),
-      ]);
-      block.traverse({
-        CallExpression: visitCallExpr,
-        VariableDeclarator: visitVariableDeclarator,
-        // do not traverse into nested blocks, or we'll hoist calls in there out to this block
-        blacklist: ['BlockStatement'],
-      });
-      callsHoistPoint.remove();
-      varsHoistPoint.remove();
-
-      function visitCallExpr(callExpr: NodePath<CallExpression>) {
-        const {
-          node: {callee},
-        } = callExpr;
-        if (
-          isIdentifier(callee) &&
-          callee.name === self.jestObjGetterIdentifier?.name
-        ) {
-          const mockStmt = callExpr.getStatementParent();
-
-          if (mockStmt) {
-            const mockStmtParent = mockStmt.parentPath;
-            if (mockStmtParent.isBlock()) {
-              const mockStmtNode = mockStmt.node;
-              mockStmt.remove();
-              callsHoistPoint.insertBefore(mockStmtNode);
+    // in `post` to make sure we come after an import transform and can unshift above the `require`s
+    post({path: program}) {
+      const self = this;
+
+      visitBlock(program);
+      program.traverse({BlockStatement: visitBlock});
+
+      function visitBlock(block: NodePath<BlockStatement> | NodePath<Program>) {
+        // use a temporary empty statement instead of the real first statement, which may itself be hoisted
+        const [varsHoistPoint, callsHoistPoint] = block.unshiftContainer(
+          'body',
+          [emptyStatement(), emptyStatement()],
+        );
+        block.traverse({
+          CallExpression: visitCallExpr,
+          VariableDeclarator: visitVariableDeclarator,
+          // do not traverse into nested blocks, or we'll hoist calls in there out to this block
+          blacklist: ['BlockStatement'],
+        });
+        callsHoistPoint.remove();
+        varsHoistPoint.remove();
+
+        function visitCallExpr(callExpr: NodePath<CallExpression>) {
+          const {
+            node: {callee},
+          } = callExpr;
+          if (
+            isIdentifier(callee) &&
+            callee.name === self.jestObjGetterIdentifier?.name
+          ) {
+            const mockStmt = callExpr.getStatementParent();
+
+            if (mockStmt) {
+              const mockStmtParent = mockStmt.parentPath;
+              if (mockStmtParent.isBlock()) {
+                const mockStmtNode = mockStmt.node;
+                mockStmt.remove();
+                callsHoistPoint.insertBefore(mockStmtNode);
+              }
             }
           }
         }
-      }
 
-      function visitVariableDeclarator(varDecl: NodePath<VariableDeclarator>) {
-        if (hoistedVariables.has(varDecl.node)) {
-          // should be assert function, but it's not. So let's cast below
-          varDecl.parentPath.assertVariableDeclaration();
-
-          const {kind, declarations} = varDecl.parent as VariableDeclaration;
-          if (declarations.length === 1) {
-            varDecl.parentPath.remove();
-          } else {
-            varDecl.remove();
+        function visitVariableDeclarator(
+          varDecl: NodePath<VariableDeclarator>,
+        ) {
+          if (hoistedVariables.has(varDecl.node)) {
+            // should be assert function, but it's not. So let's cast below
+            varDecl.parentPath.assertVariableDeclaration();
+
+            const {kind, declarations} = varDecl.parent as VariableDeclaration;
+            if (declarations.length === 1) {
+              varDecl.parentPath.remove();
+            } else {
+              varDecl.remove();
+            }
+            varsHoistPoint.insertBefore(
+              variableDeclaration(kind, [varDecl.node]),
+            );
           }
-          varsHoistPoint.insertBefore(
-            variableDeclaration(kind, [varDecl.node]),
-          );
         }
       }
-    }
-  },
-});
+    },
+  };
+}
 /* eslint-enable */

packages/diff-sequences/src/index.ts

@@ -779,12 +779,12 @@ const validateCallback = (name: string, arg: unknown) => {
 // Given lengths of sequences and input function to compare items at indexes,
 // return by output function the number of adjacent items and starting indexes
 // of each common subsequence.
-export default (
+export default function diffSequence(
   aLength: number,
   bLength: number,
   isCommon: IsCommon,
   foundSubsequence: FoundSubsequence,
-): void => {
+): void {
   validateLength('aLength', aLength);
   validateLength('bLength', bLength);
   validateCallback('isCommon', isCommon);
@@ -869,4 +869,4 @@ export default (
       foundSubsequence(nCommonR, aEnd, bEnd);
     }
   }
-};
+}

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

@@ -17,7 +17,9 @@ import {
 
 export type Expect = typeof expect;
 
-export default (config: Pick<Config.GlobalConfig, 'expand'>): Expect => {
+export default function jestExpect(
+  config: Pick<Config.GlobalConfig, 'expand'>,
+): Expect {
   expect.setState({expand: config.expand});
   expect.extend({
     toMatchInlineSnapshot,
@@ -29,4 +31,4 @@ export default (config: Pick<Config.GlobalConfig, 'expand'>): Expect => {
   expect.addSnapshotSerializer = addSerializer;
 
   return expect;
-};
+}

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

@@ -37,9 +37,9 @@ type PromptsResults = {
 
 const getConfigFilename = (ext: string) => JEST_CONFIG_BASE_NAME + ext;
 
-export default async (
+export default async function init(
   rootDir: string = tryRealpath(process.cwd()),
-): Promise<void> => {
+): Promise<void> {
   // prerequisite checks
   const projectPackageJsonPath: string = path.join(rootDir, PACKAGE_JSON);
 
@@ -152,4 +152,4 @@ export default async (
   console.log(
     `📝  Configuration file created at ${chalk.cyan(jestConfigPath)}`,
   );
-};
+}

packages/jest-config/src/resolveConfigPath.ts

@@ -21,11 +21,11 @@ const isFile = (filePath: Config.Path) =>
 
 const getConfigFilename = (ext: string) => JEST_CONFIG_BASE_NAME + ext;
 
-export default (
+export default function resolveConfigPath(
   pathToResolve: Config.Path,
   cwd: Config.Path,
   skipMultipleConfigWarning = false,
-): Config.Path => {
+): Config.Path {
   if (!path.isAbsolute(cwd)) {
     throw new Error(`"cwd" must be an absolute path. cwd: ${cwd}`);
   }
@@ -61,7 +61,7 @@ export default (
     cwd,
     skipMultipleConfigWarning,
   );
-};
+}
 
 const resolveConfigPathByTraversing = (
   pathToResolve: Config.Path,

packages/jest-console/src/getConsoleOutput.ts

@@ -14,11 +14,11 @@ import {
 } from 'jest-message-util';
 import type {ConsoleBuffer} from './types';
 
-export default (
+export default function getConsoleOutput(
   buffer: ConsoleBuffer,
   config: StackTraceConfig,
   globalConfig: Config.GlobalConfig,
-): string => {
+): string {
   const TITLE_INDENT = globalConfig.verbose ? '  ' : '    ';
   const CONSOLE_INDENT = TITLE_INDENT + '  ';
 
@@ -64,4 +64,4 @@ export default (
   }, '');
 
   return logEntries.trimRight() + '\n';
-};
+}

packages/jest-core/src/getChangedFilesPromise.ts

@@ -10,10 +10,10 @@ import type {Config} from '@jest/types';
 import {ChangedFilesPromise, getChangedFilesForRoots} from 'jest-changed-files';
 import {formatExecError} from 'jest-message-util';
 
-export default (
+export default function getChangedFilesPromise(
   globalConfig: Config.GlobalConfig,
   configs: Array<Config.ProjectConfig>,
-): ChangedFilesPromise | undefined => {
+): ChangedFilesPromise | undefined {
   if (globalConfig.onlyChanged) {
     const allRootsForAllProjects = configs.reduce<Array<Config.Path>>(
       (roots, config) => {
@@ -41,4 +41,4 @@ export default (
   }
 
   return undefined;
-};
+}

packages/jest-core/src/lib/createContext.ts

@@ -9,12 +9,14 @@ import type {Config} from '@jest/types';
 import type {HasteMapObject} from 'jest-haste-map';
 import Runtime, {Context} from 'jest-runtime';
 
-export default (
+export default function createContext(
   config: Config.ProjectConfig,
   {hasteFS, moduleMap}: HasteMapObject,
-): Context => ({
-  config,
-  hasteFS,
-  moduleMap,
-  resolver: Runtime.createResolver(config, moduleMap),
-});
+): Context {
+  return {
+    config,
+    hasteFS,
+    moduleMap,
+    resolver: Runtime.createResolver(config, moduleMap),
+  };
+}

packages/jest-core/src/lib/handleDeprecationWarnings.ts

@@ -8,11 +8,11 @@
 import chalk = require('chalk');
 import {KEYS} from 'jest-watcher';
 
-export default (
+export default function handleDeprecationWarnings(
   pipe: NodeJS.WriteStream,
   stdin: NodeJS.ReadStream = process.stdin,
-): Promise<void> =>
-  new Promise((resolve, reject) => {
+): Promise<void> {
+  return new Promise((resolve, reject) => {
     if (typeof stdin.setRawMode === 'function') {
       const messages = [
         chalk.red('There are deprecation warnings.\n'),
@@ -39,3 +39,4 @@ export default (
       resolve();
     }
   });
+}

packages/jest-core/src/lib/updateGlobalConfig.ts

@@ -13,10 +13,10 @@ type ExtraConfigOptions = Partial<
   Pick<Config.GlobalConfig, 'noSCM' | 'passWithNoTests'>
 >;
 
-export default (
+export default function updateGlobalConfig(
   globalConfig: Config.GlobalConfig,
   options: AllowedConfigOptions & ExtraConfigOptions = {},
-): Config.GlobalConfig => {
+): Config.GlobalConfig {
   const newConfig: Config.GlobalConfig = {...globalConfig};
 
   if (options.mode === 'watch') {
@@ -112,4 +112,4 @@ export default (
   }
 
   return Object.freeze(newConfig);
-};
+}