feat: allow loading .js config file with ESM syntax

README.md

@@ -106,11 +106,12 @@ Starting with v3.1 you can now use different ways of configuring lint-staged:
   - `.lintstagedrc.json`
   - `.lintstagedrc.yaml`
   - `.lintstagedrc.yml`
-  - `.lintstagedrc.mjs`
-  - `.lintstagedrc.js`
-  - `.lintstagedrc.cjs`
-- `lint-staged.config.mjs` file in ESM format
-- `lint-staged.config.js`, `.lintstagedrc.js`, or `.lintstagedrc.cjs` file in CommonJS format
+- `.lintstagedrc.mjs` or `lint-staged.config.mjs` file in ESM format
+  - the default export value should be a configuration: `export default { ... }`
+- `.lintstagedrc.cjs` or `lint-staged.config.cjs` file in CommonJS format
+  - the exports value should be a configuration: `module.exports = { ... }`
+- `lint-staged.config.js` or `.lintstagedrc.js` in either ESM or CommonJS format, depending on
+  whether your project's _package.json_ contains the `"type": "module"` option or not.
 - Pass a configuration file using the `--config` or `-c` flag
 
 See [cosmiconfig](https://github.com/davidtheclark/cosmiconfig) for more details on what formats are supported.

lib/loadConfig.js

@@ -2,6 +2,8 @@ import { cosmiconfig } from 'cosmiconfig'
 
 const dynamicImport = (path) => import(path).then((module) => module.default)
 
+const jsonParse = (path, content) => JSON.parse(content)
+
 const resolveConfig = (configPath) => {
   try {
     return require.resolve(configPath)
@@ -29,6 +31,9 @@ export const loadConfig = (configPath) => {
       'lint-staged.config.cjs',
     ],
     loaders: {
+      '.cjs': dynamicImport,
+      '.js': dynamicImport,
+      '.json': jsonParse,
       '.mjs': dynamicImport,
     },
   })

test/__mocks__/esm-config-in-js.js

@@ -0,0 +1,3 @@
+export default {
+  '*': 'mytask',
+}

test/__mocks__/my-config.cjs

@@ -0,0 +1,3 @@
+module.exports = {
+  '*': 'mytask',
+}

test/index.spec.js

@@ -128,7 +128,7 @@ describe('lintStaged', () => {
     expect(logger.printHistory()).toMatchInlineSnapshot(`""`)
   })
 
-  it('should load config file when specified', async () => {
+  it('should load JSON config file', async () => {
     expect.assertions(1)
 
     await lintStaged(
@@ -149,7 +149,7 @@ describe('lintStaged', () => {
     `)
   })
 
-  it('should parse function linter from absolute CJS config', async () => {
+  it('should load CommonJS config file from absolute path', async () => {
     expect.assertions(1)
 
     await lintStaged(
@@ -171,7 +171,7 @@ describe('lintStaged', () => {
     `)
   })
 
-  it('should parse function linter from relative CJS config', async () => {
+  it('should load CommonJS config file from relative path', async () => {
     expect.assertions(1)
 
     await lintStaged(
@@ -193,7 +193,28 @@ describe('lintStaged', () => {
     `)
   })
 
-  it('should read config from relative ESM file', async () => {
+  it('should load CommonJS config file from .cjs file', async () => {
+    expect.assertions(1)
+
+    await lintStaged(
+      {
+        configPath: path.join('test', '__mocks__', 'my-config.cjs'),
+        debug: true,
+        quiet: true,
+      },
+      logger
+    )
+
+    expect(logger.printHistory()).toMatchInlineSnapshot(`
+      "
+      LOG Running lint-staged with the following config:
+      LOG {
+        '*': 'mytask'
+      }"
+    `)
+  })
+
+  it('should load EMS config file from .mjs file', async () => {
     expect.assertions(1)
 
     await lintStaged(
@@ -214,6 +235,27 @@ describe('lintStaged', () => {
     `)
   })
 
+  it('should load EMS config file from .js file', async () => {
+    expect.assertions(1)
+
+    await lintStaged(
+      {
+        configPath: path.join('test', '__mocks__', 'esm-config-in-js.js'),
+        debug: true,
+        quiet: true,
+      },
+      logger
+    )
+
+    expect(logger.printHistory()).toMatchInlineSnapshot(`
+      "
+      LOG Running lint-staged with the following config:
+      LOG {
+        '*': 'mytask'
+      }"
+    `)
+  })
+
   it('should use config object', async () => {
     expect.assertions(1)