Add Ecmascript features tests (#65613)

Adding some tests based on this Twitter thread:
https://twitter.com/NicoloRibaudo/status/1788919867002785984

Here's what I found:

- Added a new test suite testing for:
	- Private fields
		- Turbopack: Works
		- Webpack: Works on latest
- Earlier versions of Next.js with Webpack you'd see an error failing to
parse coming from `acorn`, which webpack uses internally.
- Verified it's not failing on `next@latest` in [this
sandbox](https://codesandbox.io/p/devbox/brave-mcnulty-gszh3q?file=%2Fapp%2Fpage.tsx%3A59%2C32).
	- `import` `with { type: 'json' }`
		- Turbopack: Works
		- Webpack: Works
	- `export as` I.e. `export { x as abc }`
		- Turbopack: Works
		- Webpack:  Works
	- RegExp with `/v`
- Node.js: ⚠️ Not enabled in the test because Node.js does not support
it currently in 18.x which we run tests against.
		- Turbopack: Works
- Webpack: Fails in Webpack currently on `acorn` parsing the JavaScript


## Results

In case you want to play with the test here's a codesandbox with the
same code that is in the tests:

- `next@latest`: https://codesandbox.io/p/devbox/brave-mcnulty-gszh3q
	- Url: https://gszh3q-3000.csb.app/

Dev: Webpack
```
 PASS  test/e2e/app-dir/ecmascript-features/ecmascript-features.test.ts
  ecmascript-features
    ✓ should work using cheerio
    ✓ should work using browser
```

Build: Webpack

```
 PASS  test/e2e/app-dir/ecmascript-features/ecmascript-features.test.ts
  ecmascript-features
    ✓ should work using cheerio
    ✓ should work using browser
```

Dev: Turbopack
```
 PASS  test/e2e/app-dir/ecmascript-features/ecmascript-features.test.ts
  ecmascript-features
    ✓ should work using cheerio
    ✓ should work using browser

```

Build: Turbopack

```
 PASS  test/e2e/app-dir/ecmascript-features/ecmascript-features.test.ts
  ecmascript-features
    ✓ should work using cheerio
    ✓ should work using browser
```

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test/e2e/app-dir/ecmascript-features/turbopack/app/export-as-string/export-as-string.js

@@ -0,0 +1,5 @@
+// `.js` file as TypeScript does not support re-exporting with a string literal.
+// Details: https://github.com/microsoft/TypeScript/issues/40594
+let x = 1
+
+export { x as 'abc' }

test/e2e/app-dir/ecmascript-features/turbopack/app/export-as-string/page.js

@@ -0,0 +1,21 @@
+'use client'
+// Test both server and client compilation of ECMAScript features.
+
+import { 'abc' as x } from './export-as-string'
+
+export default function Page() {
+  return (
+    <>
+      <h1>Ecmascript features test</h1>
+      <pre id="values-to-check">
+        {JSON.stringify(
+          {
+            exportAsString: x,
+          },
+          null,
+          2
+        )}
+      </pre>
+    </>
+  )
+}

test/e2e/app-dir/ecmascript-features/turbopack/app/export-as.tsx

@@ -0,0 +1,3 @@
+let x = 1
+
+export { x as abc }

test/e2e/app-dir/ecmascript-features/turbopack/app/file.json

@@ -0,0 +1,3 @@
+{
+  "message": "Hello World"
+}

test/e2e/app-dir/ecmascript-features/turbopack/app/layout.tsx

@@ -0,0 +1,7 @@
+export default function Root({ children }: { children: React.ReactNode }) {
+  return (
+    <html>
+      <body>{children}</body>
+    </html>
+  )
+}

test/e2e/app-dir/ecmascript-features/turbopack/app/page.tsx

@@ -0,0 +1,71 @@
+'use client'
+// Test both server and client compilation of ECMAScript features.
+import { abc } from './export-as'
+import json from './file.json' with { type: 'json' }
+
+class ClassWithPrivate {
+  #privateField
+  #privateFieldWithInitializer = 11
+
+  #privateMethod() {
+    this.#privateField = 10
+  }
+
+  static #privateStaticFieldWithInitializer = 12
+
+  static #privateStaticMethod() {
+    return this.#privateStaticFieldWithInitializer
+  }
+
+  constructor() {
+    this.#privateMethod()
+  }
+
+  getPrivateField() {
+    return this.#privateField
+  }
+  getPrivateFieldWithInitializer() {
+    return this.#privateFieldWithInitializer
+  }
+  getPrivateStaticFieldWithInitializer() {
+    return ClassWithPrivate.#privateStaticFieldWithInitializer
+  }
+  getPrivateStaticMethod() {
+    return ClassWithPrivate.#privateStaticMethod()
+  }
+  isPrivateMethodAvailable() {
+    return #privateField in this
+  }
+}
+
+// Not supported in Node.js yet.
+// let regex = /abc/v
+
+export default function Page() {
+  const instance = new ClassWithPrivate()
+
+  return (
+    <>
+      <h1>Ecmascript features test</h1>
+      <pre id="values-to-check">
+        {JSON.stringify(
+          {
+            privateField: instance.getPrivateField(),
+            privateFieldWithInitializer:
+              instance.getPrivateFieldWithInitializer(),
+            privateStaticFieldWithInitializer:
+              instance.getPrivateStaticFieldWithInitializer(),
+            privateStaticMethod: instance.getPrivateStaticMethod(),
+            privateMethodInThis: instance.isPrivateMethodAvailable(),
+            exportAs: abc,
+            importWith: json.message,
+            // Not supported in Node.js yet.
+            // regex: regex instanceof RegExp
+          },
+          null,
+          2
+        )}
+      </pre>
+    </>
+  )
+}

test/e2e/app-dir/ecmascript-features/turbopack/ecmascript-features-turbopack.test.ts

@@ -0,0 +1,53 @@
+import { nextTestSetup } from 'e2e-utils'
+;(process.env.TURBOPACK ? describe : describe.skip)(
+  'ecmascript-features turbopack',
+  () => {
+    const { next } = nextTestSetup({
+      files: __dirname,
+    })
+
+    // Recommended for tests that check HTML. Cheerio is a HTML parser that has a jQuery like API.
+    it('should work using cheerio', async () => {
+      const $ = await next.render$('/')
+      expect(JSON.parse($('#values-to-check').text())).toEqual({
+        privateField: 10,
+        privateFieldWithInitializer: 11,
+        privateStaticFieldWithInitializer: 12,
+        privateStaticMethod: 12,
+        privateMethodInThis: true,
+        exportAs: 1,
+        // regex: true,
+        importWith: 'Hello World',
+      })
+
+      const $1 = await next.render$('/export-as-string')
+      expect(JSON.parse($1('#values-to-check').text())).toEqual({
+        exportAsString: 1,
+      })
+    })
+
+    // Recommended for tests that need a full browser
+    it('should work using browser', async () => {
+      const browser = await next.browser('/')
+      expect(
+        JSON.parse(await browser.elementByCss('#values-to-check').text())
+      ).toEqual({
+        privateField: 10,
+        privateFieldWithInitializer: 11,
+        privateStaticFieldWithInitializer: 12,
+        privateStaticMethod: 12,
+        privateMethodInThis: true,
+        exportAs: 1,
+        // regex: true,
+        importWith: 'Hello World',
+      })
+
+      const browser2 = await next.browser('/export-as-string')
+      expect(
+        JSON.parse(await browser2.elementByCss('#values-to-check').text())
+      ).toEqual({
+        exportAsString: 1,
+      })
+    })
+  }
+)

test/e2e/app-dir/ecmascript-features/turbopack/next.config.js

@@ -0,0 +1,6 @@
+/**
+ * @type {import('next').NextConfig}
+ */
+const nextConfig = {}
+
+module.exports = nextConfig

test/e2e/app-dir/ecmascript-features/webpack/app/export-as-string/_todo-page.js

@@ -0,0 +1,21 @@
+'use client'
+// Test both server and client compilation of ECMAScript features.
+
+import { 'abc' as x } from './export-as-string'
+
+export default function Page() {
+  return (
+    <>
+      <h1>Ecmascript features test</h1>
+      <pre id="values-to-check">
+        {JSON.stringify(
+          {
+            exportAsString: x,
+          },
+          null,
+          2
+        )}
+      </pre>
+    </>
+  )
+}

test/e2e/app-dir/ecmascript-features/webpack/app/export-as-string/export-as-string.js

@@ -0,0 +1,6 @@
+// `.js` file as TypeScript does not support re-exporting with a string literal.
+// Details: https://github.com/microsoft/TypeScript/issues/40594
+
+let x = 1
+
+export { x as 'abc' }

test/e2e/app-dir/ecmascript-features/webpack/app/export-as.tsx

@@ -0,0 +1,3 @@
+let x = 1
+
+export { x as abc }

test/e2e/app-dir/ecmascript-features/webpack/app/file.json

@@ -0,0 +1,3 @@
+{
+  "message": "Hello World"
+}

test/e2e/app-dir/ecmascript-features/webpack/app/layout.tsx

@@ -0,0 +1,7 @@
+export default function Root({ children }: { children: React.ReactNode }) {
+  return (
+    <html>
+      <body>{children}</body>
+    </html>
+  )
+}

test/e2e/app-dir/ecmascript-features/webpack/app/page.tsx

@@ -0,0 +1,73 @@
+'use client'
+// Test both server and client compilation of ECMAScript features.
+import { abc } from './export-as'
+import json from './file.json' with { type: 'json' }
+
+class ClassWithPrivate {
+  #privateField
+  #privateFieldWithInitializer = 11
+
+  #privateMethod() {
+    this.#privateField = 10
+  }
+
+  static #privateStaticFieldWithInitializer = 12
+
+  static #privateStaticMethod() {
+    return this.#privateStaticFieldWithInitializer
+  }
+
+  constructor() {
+    this.#privateMethod()
+  }
+
+  getPrivateField() {
+    return this.#privateField
+  }
+  getPrivateFieldWithInitializer() {
+    return this.#privateFieldWithInitializer
+  }
+  getPrivateStaticFieldWithInitializer() {
+    return ClassWithPrivate.#privateStaticFieldWithInitializer
+  }
+  getPrivateStaticMethod() {
+    return ClassWithPrivate.#privateStaticMethod()
+  }
+  // TODO: Not supported in webpack yet.
+  // isPrivateMethodAvailable() {
+  //   return #privateField in this
+  // }
+}
+
+// Not supported in Node.js yet.
+// let regex = /abc/v
+
+export default function Page() {
+  const instance = new ClassWithPrivate()
+
+  return (
+    <>
+      <h1>Ecmascript features test</h1>
+      <pre id="values-to-check">
+        {JSON.stringify(
+          {
+            privateField: instance.getPrivateField(),
+            privateFieldWithInitializer:
+              instance.getPrivateFieldWithInitializer(),
+            privateStaticFieldWithInitializer:
+              instance.getPrivateStaticFieldWithInitializer(),
+            privateStaticMethod: instance.getPrivateStaticMethod(),
+            // TODO: Not supported in webpack yet.
+            // privateMethodInThis: instance.isPrivateMethodAvailable(),
+            exportAs: abc,
+            importWith: json.message,
+            // Not supported in Node.js yet.
+            // regex: regex instanceof RegExp
+          },
+          null,
+          2
+        )}
+      </pre>
+    </>
+  )
+}

test/e2e/app-dir/ecmascript-features/webpack/ecmascript-features-webpack.test.ts

@@ -0,0 +1,55 @@
+import { nextTestSetup } from 'e2e-utils'
+;(process.env.TURBOPACK ? describe.skip : describe)(
+  'ecmascript-features webpack',
+  () => {
+    const { next } = nextTestSetup({
+      files: __dirname,
+    })
+
+    // Recommended for tests that check HTML. Cheerio is a HTML parser that has a jQuery like API.
+    it('should work using cheerio', async () => {
+      const $ = await next.render$('/')
+      expect(JSON.parse($('#values-to-check').text())).toEqual({
+        privateField: 10,
+        privateFieldWithInitializer: 11,
+        privateStaticFieldWithInitializer: 12,
+        privateStaticMethod: 12,
+        // privateMethodInThis: true,
+        exportAs: 1,
+        // regex: true,
+        importWith: 'Hello World',
+      })
+
+      // TODO: `export { x as "abc" }` (export as string) is not supported in webpack yet.
+      // const $1 = await next.render$('/export-as-string')
+      // expect(JSON.parse($1('#values-to-check').text())).toEqual({
+      //   exportAsString: 1,
+      // })
+    })
+
+    // Recommended for tests that need a full browser
+    it('should work using browser', async () => {
+      const browser = await next.browser('/')
+      expect(
+        JSON.parse(await browser.elementByCss('#values-to-check').text())
+      ).toEqual({
+        privateField: 10,
+        privateFieldWithInitializer: 11,
+        privateStaticFieldWithInitializer: 12,
+        privateStaticMethod: 12,
+        // privateMethodInThis: true,
+        exportAs: 1,
+        // regex: true,
+        importWith: 'Hello World',
+      })
+
+      // TODO: `export { x as "abc" }` (export as string) is not supported in webpack yet.
+      // const browser2 = await next.browser('/export-as-string')
+      // expect(
+      //   JSON.parse(await browser2.elementByCss('#values-to-check').text())
+      // ).toEqual({
+      //   exportAsString: 1,
+      // })
+    })
+  }
+)

test/e2e/app-dir/ecmascript-features/webpack/next.config.js

@@ -0,0 +1,6 @@
+/**
+ * @type {import('next').NextConfig}
+ */
+const nextConfig = {}
+
+module.exports = nextConfig