Add More Configuration File Options

packages/next/lib/find-config.ts

@@ -23,12 +23,23 @@ export async function findConfig<T>(
   }
 
   // If we didn't find the configuration in `package.json`, we should look for
-  // known filenames. The /rc$/ version of this file does not support YAML
-  // like some configuration loaders.
-  const filePath = await findUp(`.${key}rc.json`, {
-    cwd: directory,
-  })
+  // known filenames.
+  const filePath = await findUp(
+    [
+      `.${key}rc.json`,
+      `${key}.config.json`,
+      `.${key}rc.js`,
+      `${key}.config.js`,
+    ],
+    {
+      cwd: directory,
+    }
+  )
   if (filePath) {
+    if (filePath.endsWith('.js')) {
+      return require(filePath)
+    }
+
     // We load JSON contents with JSON5 to allow users to comment in their
     // configuration file. This pattern was popularized by TypeScript.
     const fileContents = fs.readFileSync(filePath, 'utf8')

test/unit/find-config.test.js

@@ -10,6 +10,24 @@ describe('find config', () => {
     expect(config).toEqual({ foo: 'bar' })
   })
 
+  it('should resolve rc.js', async () => {
+    const config = await findConfig(join(fixtureDir, 'config-js'), 'test')
+    expect(config).toEqual({ foo: 'bar' })
+  })
+
+  it('should resolve .config.json', async () => {
+    const config = await findConfig(
+      join(fixtureDir, 'config-long-json'),
+      'test'
+    )
+    expect(config).toEqual({ foo: 'bar' })
+  })
+
+  it('should resolve .config.js', async () => {
+    const config = await findConfig(join(fixtureDir, 'config-long-js'), 'test')
+    expect(config).toEqual({ foo: 'bar' })
+  })
+
   it('should resolve package.json', async () => {
     const config = await findConfig(
       join(fixtureDir, 'config-package-json'),

test/unit/fixtures/config-js/.testrc.js

@@ -0,0 +1 @@
+module.exports = { foo: 'bar' }

test/unit/fixtures/config-long-js/test.config.js

@@ -0,0 +1 @@
+module.exports = { foo: 'bar' }

test/unit/fixtures/config-long-json/test.config.json

@@ -0,0 +1 @@
+{ "foo": "bar" }