diff --git a/packages/docusaurus-utils/src/__tests__/dataFileUtils.test.ts b/packages/docusaurus-utils/src/__tests__/dataFileUtils.test.ts
index 54f92601cc..f58a155e99 100644
--- a/packages/docusaurus-utils/src/__tests__/dataFileUtils.test.ts
+++ b/packages/docusaurus-utils/src/__tests__/dataFileUtils.test.ts
@@ -173,7 +173,7 @@ describe('findFolderContainingFile', () => {
     await expect(
       findFolderContainingFile(
         ['/abcdef', '/gehij', __dirname, '/klmn'],
-        'index.test.ts',
+        'dataFileUtils.test.ts',
       ),
     ).resolves.toEqual(__dirname);
   });
@@ -190,16 +190,19 @@ describe('getFolderContainingFile', () => {
     await expect(
       getFolderContainingFile(
         ['/abcdef', '/gehij', __dirname, '/klmn'],
-        'index.test.ts',
+        'dataFileUtils.test.ts',
       ),
     ).resolves.toEqual(__dirname);
   });
 
   test('throw if no folder contain such file', async () => {
     await expect(
-      getFolderContainingFile(['/abcdef', '/gehij', '/klmn'], 'index.test.ts'),
+      getFolderContainingFile(
+        ['/abcdef', '/gehij', '/klmn'],
+        'dataFileUtils.test.ts',
+      ),
     ).rejects.toThrowErrorMatchingInlineSnapshot(`
-            "File \\"index.test.ts\\" does not exist in any of these folders:
+            "File \\"dataFileUtils.test.ts\\" does not exist in any of these folders:
             - /abcdef
             - /gehij
             - /klmn]"
diff --git a/packages/docusaurus-utils/src/__tests__/emitUtils.test.ts b/packages/docusaurus-utils/src/__tests__/emitUtils.test.ts
new file mode 100644
index 0000000000..938bb5007d
--- /dev/null
+++ b/packages/docusaurus-utils/src/__tests__/emitUtils.test.ts
@@ -0,0 +1,154 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {genChunkName, readOutputHTMLFile, generate} from '../emitUtils';
+import path from 'path';
+import fs from 'fs-extra';
+
+test('genChunkName', () => {
+  const firstAssert: Record<string, string> = {
+    '/docs/adding-blog': 'docs-adding-blog-062',
+    '/docs/versioning': 'docs-versioning-8a8',
+    '/': 'index',
+    '/blog/2018/04/30/How-I-Converted-Profilo-To-Docusaurus':
+      'blog-2018-04-30-how-i-converted-profilo-to-docusaurus-4f2',
+    '/youtube': 'youtube-429',
+    '/users/en/': 'users-en-f7a',
+    '/blog': 'blog-c06',
+  };
+  Object.keys(firstAssert).forEach((str) => {
+    expect(genChunkName(str)).toBe(firstAssert[str]);
+  });
+
+  // Don't allow different chunk name for same path.
+  expect(genChunkName('path/is/similar', 'oldPrefix')).toEqual(
+    genChunkName('path/is/similar', 'newPrefix'),
+  );
+
+  // Even with same preferred name, still different chunk name for
+  // different path
+  const secondAssert: Record<string, string> = {
+    '/blog/1': 'blog-85-f-089',
+    '/blog/2': 'blog-353-489',
+  };
+  Object.keys(secondAssert).forEach((str) => {
+    expect(genChunkName(str, undefined, 'blog')).toBe(secondAssert[str]);
+  });
+
+  // Only generate short unique id
+  const thirdAssert: Record<string, string> = {
+    a: '0cc175b9',
+    b: '92eb5ffe',
+    c: '4a8a08f0',
+    d: '8277e091',
+  };
+  Object.keys(thirdAssert).forEach((str) => {
+    expect(genChunkName(str, undefined, undefined, true)).toBe(
+      thirdAssert[str],
+    );
+  });
+  expect(genChunkName('d', undefined, undefined, true)).toBe('8277e091');
+});
+
+describe('readOutputHTMLFile', () => {
+  test('trailing slash undefined', async () => {
+    await expect(
+      readOutputHTMLFile(
+        '/file',
+        path.join(__dirname, '__fixtures__/build-snap'),
+        undefined,
+      ).then(String),
+    ).resolves.toEqual('file\n');
+    await expect(
+      readOutputHTMLFile(
+        '/folder',
+        path.join(__dirname, '__fixtures__/build-snap'),
+        undefined,
+      ).then(String),
+    ).resolves.toEqual('folder\n');
+    await expect(
+      readOutputHTMLFile(
+        '/file/',
+        path.join(__dirname, '__fixtures__/build-snap'),
+        undefined,
+      ).then(String),
+    ).resolves.toEqual('file\n');
+    await expect(
+      readOutputHTMLFile(
+        '/folder/',
+        path.join(__dirname, '__fixtures__/build-snap'),
+        undefined,
+      ).then(String),
+    ).resolves.toEqual('folder\n');
+  });
+  test('trailing slash true', async () => {
+    await expect(
+      readOutputHTMLFile(
+        '/folder',
+        path.join(__dirname, '__fixtures__/build-snap'),
+        true,
+      ).then(String),
+    ).resolves.toEqual('folder\n');
+    await expect(
+      readOutputHTMLFile(
+        '/folder/',
+        path.join(__dirname, '__fixtures__/build-snap'),
+        true,
+      ).then(String),
+    ).resolves.toEqual('folder\n');
+  });
+  test('trailing slash false', async () => {
+    await expect(
+      readOutputHTMLFile(
+        '/file',
+        path.join(__dirname, '__fixtures__/build-snap'),
+        false,
+      ).then(String),
+    ).resolves.toEqual('file\n');
+    await expect(
+      readOutputHTMLFile(
+        '/file/',
+        path.join(__dirname, '__fixtures__/build-snap'),
+        false,
+      ).then(String),
+    ).resolves.toEqual('file\n');
+  });
+});
+
+test('generate', async () => {
+  const writeMock = jest.spyOn(fs, 'writeFile').mockImplementation(() => {});
+  const existsMock = jest.spyOn(fs, 'pathExists');
+  const readMock = jest.spyOn(fs, 'readFile');
+
+  // First call: no file, no cache
+  existsMock.mockImplementationOnce(() => false);
+  await generate(__dirname, 'foo', 'bar');
+  expect(writeMock).toHaveBeenNthCalledWith(
+    1,
+    path.join(__dirname, 'foo'),
+    'bar',
+  );
+
+  // Second call: cache exists
+  await generate(__dirname, 'foo', 'bar');
+  expect(writeMock).toBeCalledTimes(1);
+
+  // Generate another: file exists, cache doesn't
+  existsMock.mockImplementationOnce(() => true);
+  // @ts-expect-error: seems the typedef doesn't understand overload
+  readMock.mockImplementationOnce(() => Promise.resolve('bar'));
+  await generate(__dirname, 'baz', 'bar');
+  expect(writeMock).toBeCalledTimes(1);
+
+  // Generate again: force skip cache
+  await generate(__dirname, 'foo', 'bar', true);
+  expect(writeMock).toHaveBeenNthCalledWith(
+    2,
+    path.join(__dirname, 'foo'),
+    'bar',
+  );
+});
diff --git a/packages/docusaurus-utils/src/__tests__/i18nUtils.test.ts b/packages/docusaurus-utils/src/__tests__/i18nUtils.test.ts
new file mode 100644
index 0000000000..39fc8aae7b
--- /dev/null
+++ b/packages/docusaurus-utils/src/__tests__/i18nUtils.test.ts
@@ -0,0 +1,91 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {
+  mergeTranslations,
+  updateTranslationFileMessages,
+  getPluginI18nPath,
+} from '../i18nUtils';
+
+test('mergeTranslations', () => {
+  expect(
+    mergeTranslations([
+      {
+        T1: {message: 'T1 message', description: 'T1 desc'},
+        T2: {message: 'T2 message', description: 'T2 desc'},
+        T3: {message: 'T3 message', description: 'T3 desc'},
+      },
+      {
+        T4: {message: 'T4 message', description: 'T4 desc'},
+      },
+      {T2: {message: 'T2 message 2', description: 'T2 desc 2'}},
+    ]),
+  ).toEqual({
+    T1: {message: 'T1 message', description: 'T1 desc'},
+    T2: {message: 'T2 message 2', description: 'T2 desc 2'},
+    T3: {message: 'T3 message', description: 'T3 desc'},
+    T4: {message: 'T4 message', description: 'T4 desc'},
+  });
+});
+
+test('updateTranslationFileMessages', () => {
+  expect(
+    updateTranslationFileMessages(
+      {
+        path: 'abc',
+        content: {
+          t1: {message: 't1 message', description: 't1 desc'},
+          t2: {message: 't2 message', description: 't2 desc'},
+          t3: {message: 't3 message', description: 't3 desc'},
+        },
+      },
+      (message) => `prefix ${message} suffix`,
+    ),
+  ).toEqual({
+    path: 'abc',
+    content: {
+      t1: {message: 'prefix t1 message suffix', description: 't1 desc'},
+      t2: {message: 'prefix t2 message suffix', description: 't2 desc'},
+      t3: {message: 'prefix t3 message suffix', description: 't3 desc'},
+    },
+  });
+});
+
+describe('getPluginI18nPath', () => {
+  test('gets correct path', () => {
+    expect(
+      getPluginI18nPath({
+        siteDir: __dirname,
+        locale: 'zh-Hans',
+        pluginName: 'plugin-content-docs',
+        pluginId: 'community',
+        subPaths: ['foo'],
+      }),
+    ).toMatchInlineSnapshot(
+      `"<PROJECT_ROOT>/packages/docusaurus-utils/src/__tests__/i18n/zh-Hans/plugin-content-docs-community/foo"`,
+    );
+  });
+  test('gets correct path for default plugin', () => {
+    expect(
+      getPluginI18nPath({
+        siteDir: __dirname,
+        locale: 'zh-Hans',
+        pluginName: 'plugin-content-docs',
+        subPaths: ['foo'],
+      }).replace(__dirname, ''),
+    ).toMatchInlineSnapshot(`"/i18n/zh-Hans/plugin-content-docs/foo"`);
+  });
+  test('gets correct path when no subpaths', () => {
+    expect(
+      getPluginI18nPath({
+        siteDir: __dirname,
+        locale: 'zh-Hans',
+        pluginName: 'plugin-content-docs',
+      }).replace(__dirname, ''),
+    ).toMatchInlineSnapshot(`"/i18n/zh-Hans/plugin-content-docs"`);
+  });
+});
diff --git a/packages/docusaurus-utils/src/__tests__/index.test.ts b/packages/docusaurus-utils/src/__tests__/index.test.ts
deleted file mode 100644
index 8dbc0bc117..0000000000
--- a/packages/docusaurus-utils/src/__tests__/index.test.ts
+++ /dev/null
@@ -1,529 +0,0 @@
-/**
- * Copyright (c) Facebook, Inc. and its affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- */
-
-import {
-  fileToPath,
-  genChunkName,
-  isValidPathname,
-  addTrailingSlash,
-  removeTrailingSlash,
-  removeSuffix,
-  removePrefix,
-  addLeadingSlash,
-  getElementsAround,
-  mergeTranslations,
-  mapAsyncSequential,
-  findAsyncSequential,
-  updateTranslationFileMessages,
-  encodePath,
-  addTrailingPathSeparator,
-  resolvePathname,
-  getPluginI18nPath,
-  generate,
-  reportMessage,
-  posixPath,
-  readOutputHTMLFile,
-} from '../index';
-import _ from 'lodash';
-import fs from 'fs-extra';
-import path from 'path';
-
-describe('load utils', () => {
-  test('fileToPath', () => {
-    const asserts: Record<string, string> = {
-      'index.md': '/',
-      'hello/index.md': '/hello/',
-      'foo.md': '/foo',
-      'foo/bar.md': '/foo/bar',
-      'index.js': '/',
-      'hello/index.js': '/hello/',
-      'foo.js': '/foo',
-      'foo/bar.js': '/foo/bar',
-    };
-    Object.keys(asserts).forEach((file) => {
-      expect(fileToPath(file)).toBe(asserts[file]);
-    });
-  });
-
-  test('encodePath', () => {
-    expect(encodePath('a/foo/')).toEqual('a/foo/');
-    expect(encodePath('a/<foo>/')).toEqual('a/%3Cfoo%3E/');
-    expect(encodePath('a/你好/')).toEqual('a/%E4%BD%A0%E5%A5%BD/');
-  });
-
-  test('genChunkName', () => {
-    const firstAssert: Record<string, string> = {
-      '/docs/adding-blog': 'docs-adding-blog-062',
-      '/docs/versioning': 'docs-versioning-8a8',
-      '/': 'index',
-      '/blog/2018/04/30/How-I-Converted-Profilo-To-Docusaurus':
-        'blog-2018-04-30-how-i-converted-profilo-to-docusaurus-4f2',
-      '/youtube': 'youtube-429',
-      '/users/en/': 'users-en-f7a',
-      '/blog': 'blog-c06',
-    };
-    Object.keys(firstAssert).forEach((str) => {
-      expect(genChunkName(str)).toBe(firstAssert[str]);
-    });
-
-    // Don't allow different chunk name for same path.
-    expect(genChunkName('path/is/similar', 'oldPrefix')).toEqual(
-      genChunkName('path/is/similar', 'newPrefix'),
-    );
-
-    // Even with same preferred name, still different chunk name for
-    // different path
-    const secondAssert: Record<string, string> = {
-      '/blog/1': 'blog-85-f-089',
-      '/blog/2': 'blog-353-489',
-    };
-    Object.keys(secondAssert).forEach((str) => {
-      expect(genChunkName(str, undefined, 'blog')).toBe(secondAssert[str]);
-    });
-
-    // Only generate short unique id
-    const thirdAssert: Record<string, string> = {
-      a: '0cc175b9',
-      b: '92eb5ffe',
-      c: '4a8a08f0',
-      d: '8277e091',
-    };
-    Object.keys(thirdAssert).forEach((str) => {
-      expect(genChunkName(str, undefined, undefined, true)).toBe(
-        thirdAssert[str],
-      );
-    });
-    expect(genChunkName('d', undefined, undefined, true)).toBe('8277e091');
-  });
-
-  test('addTrailingPathSeparator', () => {
-    expect(addTrailingPathSeparator('foo')).toEqual(
-      process.platform === 'win32' ? 'foo\\' : 'foo/',
-    );
-    expect(addTrailingPathSeparator('foo/')).toEqual(
-      process.platform === 'win32' ? 'foo\\' : 'foo/',
-    );
-  });
-
-  test('resolvePathname', () => {
-    // These tests are directly copied from https://github.com/mjackson/resolve-pathname/blob/master/modules/__tests__/resolvePathname-test.js
-    // Maybe we want to wrap that logic in the future?
-    expect(resolvePathname('c')).toEqual('c');
-    expect(resolvePathname('c', 'a/b')).toEqual('a/c');
-    expect(resolvePathname('/c', '/a/b')).toEqual('/c');
-    expect(resolvePathname('', '/a/b')).toEqual('/a/b');
-    expect(resolvePathname('../c', '/a/b')).toEqual('/c');
-    expect(resolvePathname('c', '/a/b')).toEqual('/a/c');
-    expect(resolvePathname('c', '/a/')).toEqual('/a/c');
-    expect(resolvePathname('..', '/a/b')).toEqual('/');
-  });
-
-  test('isValidPathname', () => {
-    expect(isValidPathname('/')).toBe(true);
-    expect(isValidPathname('/hey')).toBe(true);
-    expect(isValidPathname('/hey/ho')).toBe(true);
-    expect(isValidPathname('/hey/ho/')).toBe(true);
-    expect(isValidPathname('/hey/h%C3%B4/')).toBe(true);
-    expect(isValidPathname('/hey///ho///')).toBe(true); // Unexpected but valid
-    expect(isValidPathname('/hey/héllô you')).toBe(true);
-
-    expect(isValidPathname('')).toBe(false);
-    expect(isValidPathname('hey')).toBe(false);
-    expect(isValidPathname('/hey?qs=ho')).toBe(false);
-    expect(isValidPathname('https://fb.com/hey')).toBe(false);
-    expect(isValidPathname('//hey')).toBe(false);
-    expect(isValidPathname('////')).toBe(false);
-  });
-});
-
-describe('generate', () => {
-  test('behaves correctly', async () => {
-    const writeMock = jest.spyOn(fs, 'writeFile').mockImplementation(() => {});
-    const existsMock = jest.spyOn(fs, 'pathExists');
-    const readMock = jest.spyOn(fs, 'readFile');
-
-    // First call: no file, no cache
-    existsMock.mockImplementationOnce(() => false);
-    await generate(__dirname, 'foo', 'bar');
-    expect(writeMock).toHaveBeenNthCalledWith(
-      1,
-      path.join(__dirname, 'foo'),
-      'bar',
-    );
-
-    // Second call: cache exists
-    await generate(__dirname, 'foo', 'bar');
-    expect(writeMock).toBeCalledTimes(1);
-
-    // Generate another: file exists, cache doesn't
-    existsMock.mockImplementationOnce(() => true);
-    // @ts-expect-error: seems the typedef doesn't understand overload
-    readMock.mockImplementationOnce(() => Promise.resolve('bar'));
-    await generate(__dirname, 'baz', 'bar');
-    expect(writeMock).toBeCalledTimes(1);
-
-    // Generate again: force skip cache
-    await generate(__dirname, 'foo', 'bar', true);
-    expect(writeMock).toHaveBeenNthCalledWith(
-      2,
-      path.join(__dirname, 'foo'),
-      'bar',
-    );
-  });
-});
-
-describe('addTrailingSlash', () => {
-  test('should no-op', () => {
-    expect(addTrailingSlash('/abcd/')).toEqual('/abcd/');
-  });
-  test('should add /', () => {
-    expect(addTrailingSlash('/abcd')).toEqual('/abcd/');
-  });
-});
-
-describe('addLeadingSlash', () => {
-  test('should no-op', () => {
-    expect(addLeadingSlash('/abc')).toEqual('/abc');
-  });
-  test('should add /', () => {
-    expect(addLeadingSlash('abc')).toEqual('/abc');
-  });
-});
-
-describe('removeTrailingSlash', () => {
-  test('should no-op', () => {
-    expect(removeTrailingSlash('/abcd')).toEqual('/abcd');
-  });
-  test('should remove /', () => {
-    expect(removeTrailingSlash('/abcd/')).toEqual('/abcd');
-  });
-});
-
-describe('removeSuffix', () => {
-  test('should no-op 1', () => {
-    expect(removeSuffix('abcdef', 'ijk')).toEqual('abcdef');
-  });
-  test('should no-op 2', () => {
-    expect(removeSuffix('abcdef', 'abc')).toEqual('abcdef');
-  });
-  test('should no-op 3', () => {
-    expect(removeSuffix('abcdef', '')).toEqual('abcdef');
-  });
-  test('should remove suffix', () => {
-    expect(removeSuffix('abcdef', 'ef')).toEqual('abcd');
-  });
-});
-
-describe('removePrefix', () => {
-  test('should no-op 1', () => {
-    expect(removePrefix('abcdef', 'ijk')).toEqual('abcdef');
-  });
-  test('should no-op 2', () => {
-    expect(removePrefix('abcdef', 'def')).toEqual('abcdef');
-  });
-  test('should no-op 3', () => {
-    expect(removePrefix('abcdef', '')).toEqual('abcdef');
-  });
-  test('should remove prefix', () => {
-    expect(removePrefix('abcdef', 'ab')).toEqual('cdef');
-  });
-});
-
-describe('getElementsAround', () => {
-  test('can return elements around', () => {
-    expect(getElementsAround(['a', 'b', 'c', 'd'], 0)).toEqual({
-      previous: undefined,
-      next: 'b',
-    });
-    expect(getElementsAround(['a', 'b', 'c', 'd'], 1)).toEqual({
-      previous: 'a',
-      next: 'c',
-    });
-    expect(getElementsAround(['a', 'b', 'c', 'd'], 2)).toEqual({
-      previous: 'b',
-      next: 'd',
-    });
-    expect(getElementsAround(['a', 'b', 'c', 'd'], 3)).toEqual({
-      previous: 'c',
-      next: undefined,
-    });
-  });
-
-  test('throws if bad index is provided', () => {
-    expect(() =>
-      getElementsAround(['a', 'b', 'c', 'd'], -1),
-    ).toThrowErrorMatchingInlineSnapshot(
-      `"Valid \\"aroundIndex\\" for array (of size 4) are between 0 and 3, but you provided -1."`,
-    );
-    expect(() =>
-      getElementsAround(['a', 'b', 'c', 'd'], 4),
-    ).toThrowErrorMatchingInlineSnapshot(
-      `"Valid \\"aroundIndex\\" for array (of size 4) are between 0 and 3, but you provided 4."`,
-    );
-  });
-});
-
-describe('mergeTranslations', () => {
-  test('should merge translations', () => {
-    expect(
-      mergeTranslations([
-        {
-          T1: {message: 'T1 message', description: 'T1 desc'},
-          T2: {message: 'T2 message', description: 'T2 desc'},
-          T3: {message: 'T3 message', description: 'T3 desc'},
-        },
-        {
-          T4: {message: 'T4 message', description: 'T4 desc'},
-        },
-        {T2: {message: 'T2 message 2', description: 'T2 desc 2'}},
-      ]),
-    ).toEqual({
-      T1: {message: 'T1 message', description: 'T1 desc'},
-      T2: {message: 'T2 message 2', description: 'T2 desc 2'},
-      T3: {message: 'T3 message', description: 'T3 desc'},
-      T4: {message: 'T4 message', description: 'T4 desc'},
-    });
-  });
-});
-
-describe('mapAsyncSequential', () => {
-  function sleep(timeout: number): Promise<void> {
-    return new Promise((resolve) => {
-      setTimeout(resolve, timeout);
-    });
-  }
-
-  test('map sequentially', async () => {
-    const itemToTimeout: Record<string, number> = {
-      '1': 50,
-      '2': 150,
-      '3': 100,
-    };
-    const items = Object.keys(itemToTimeout);
-
-    const itemMapStartsAt: Record<string, number> = {};
-    const itemMapEndsAt: Record<string, number> = {};
-
-    const timeBefore = Date.now();
-    await expect(
-      mapAsyncSequential(items, async (item) => {
-        const itemTimeout = itemToTimeout[item];
-        itemMapStartsAt[item] = Date.now();
-        await sleep(itemTimeout);
-        itemMapEndsAt[item] = Date.now();
-        return `${item} mapped`;
-      }),
-    ).resolves.toEqual(['1 mapped', '2 mapped', '3 mapped']);
-    const timeAfter = Date.now();
-
-    const timeTotal = timeAfter - timeBefore;
-
-    const totalTimeouts = _.sum(Object.values(itemToTimeout));
-    expect(timeTotal).toBeGreaterThanOrEqual(totalTimeouts - 20);
-
-    expect(itemMapStartsAt['1']).toBeGreaterThanOrEqual(0);
-    expect(itemMapStartsAt['2']).toBeGreaterThanOrEqual(
-      itemMapEndsAt['1'] - 20,
-    );
-    expect(itemMapStartsAt['3']).toBeGreaterThanOrEqual(
-      itemMapEndsAt['2'] - 20,
-    );
-  });
-});
-
-describe('findAsyncSequential', () => {
-  function sleep(timeout: number): Promise<void> {
-    return new Promise((resolve) => {
-      setTimeout(resolve, timeout);
-    });
-  }
-
-  test('find sequentially', async () => {
-    const items = ['1', '2', '3'];
-
-    const findFn = jest.fn(async (item: string) => {
-      await sleep(50);
-      return item === '2';
-    });
-
-    const timeBefore = Date.now();
-    await expect(findAsyncSequential(items, findFn)).resolves.toEqual('2');
-    const timeAfter = Date.now();
-
-    expect(findFn).toHaveBeenCalledTimes(2);
-    expect(findFn).toHaveBeenNthCalledWith(1, '1');
-    expect(findFn).toHaveBeenNthCalledWith(2, '2');
-
-    const timeTotal = timeAfter - timeBefore;
-    expect(timeTotal).toBeGreaterThanOrEqual(80);
-    expect(timeTotal).toBeLessThan(120);
-  });
-});
-
-describe('readOutputHTMLFile', () => {
-  test('trailing slash undefined', async () => {
-    await expect(
-      readOutputHTMLFile(
-        '/file',
-        path.join(__dirname, '__fixtures__/build-snap'),
-        undefined,
-      ).then(String),
-    ).resolves.toEqual('file\n');
-    await expect(
-      readOutputHTMLFile(
-        '/folder',
-        path.join(__dirname, '__fixtures__/build-snap'),
-        undefined,
-      ).then(String),
-    ).resolves.toEqual('folder\n');
-    await expect(
-      readOutputHTMLFile(
-        '/file/',
-        path.join(__dirname, '__fixtures__/build-snap'),
-        undefined,
-      ).then(String),
-    ).resolves.toEqual('file\n');
-    await expect(
-      readOutputHTMLFile(
-        '/folder/',
-        path.join(__dirname, '__fixtures__/build-snap'),
-        undefined,
-      ).then(String),
-    ).resolves.toEqual('folder\n');
-  });
-  test('trailing slash true', async () => {
-    await expect(
-      readOutputHTMLFile(
-        '/folder',
-        path.join(__dirname, '__fixtures__/build-snap'),
-        true,
-      ).then(String),
-    ).resolves.toEqual('folder\n');
-    await expect(
-      readOutputHTMLFile(
-        '/folder/',
-        path.join(__dirname, '__fixtures__/build-snap'),
-        true,
-      ).then(String),
-    ).resolves.toEqual('folder\n');
-  });
-  test('trailing slash false', async () => {
-    await expect(
-      readOutputHTMLFile(
-        '/file',
-        path.join(__dirname, '__fixtures__/build-snap'),
-        false,
-      ).then(String),
-    ).resolves.toEqual('file\n');
-    await expect(
-      readOutputHTMLFile(
-        '/file/',
-        path.join(__dirname, '__fixtures__/build-snap'),
-        false,
-      ).then(String),
-    ).resolves.toEqual('file\n');
-  });
-});
-
-describe('updateTranslationFileMessages', () => {
-  test('should update messages', () => {
-    expect(
-      updateTranslationFileMessages(
-        {
-          path: 'abc',
-          content: {
-            t1: {message: 't1 message', description: 't1 desc'},
-            t2: {message: 't2 message', description: 't2 desc'},
-            t3: {message: 't3 message', description: 't3 desc'},
-          },
-        },
-        (message) => `prefix ${message} suffix`,
-      ),
-    ).toEqual({
-      path: 'abc',
-      content: {
-        t1: {message: 'prefix t1 message suffix', description: 't1 desc'},
-        t2: {message: 'prefix t2 message suffix', description: 't2 desc'},
-        t3: {message: 'prefix t3 message suffix', description: 't3 desc'},
-      },
-    });
-  });
-});
-
-describe('getPluginI18nPath', () => {
-  test('gets correct path', () => {
-    expect(
-      posixPath(
-        getPluginI18nPath({
-          siteDir: __dirname,
-          locale: 'zh-Hans',
-          pluginName: 'plugin-content-docs',
-          pluginId: 'community',
-          subPaths: ['foo'],
-        }).replace(__dirname, ''),
-      ),
-    ).toEqual('/i18n/zh-Hans/plugin-content-docs-community/foo');
-  });
-  test('gets correct path for default plugin', () => {
-    expect(
-      posixPath(
-        getPluginI18nPath({
-          siteDir: __dirname,
-          locale: 'zh-Hans',
-          pluginName: 'plugin-content-docs',
-          subPaths: ['foo'],
-        }).replace(__dirname, ''),
-      ),
-    ).toEqual('/i18n/zh-Hans/plugin-content-docs/foo');
-  });
-  test('gets correct path when no subpaths', () => {
-    expect(
-      posixPath(
-        getPluginI18nPath({
-          siteDir: __dirname,
-          locale: 'zh-Hans',
-          pluginName: 'plugin-content-docs',
-        }).replace(__dirname, ''),
-      ),
-    ).toEqual('/i18n/zh-Hans/plugin-content-docs');
-  });
-});
-
-describe('reportMessage', () => {
-  test('all severities', () => {
-    const consoleLog = jest.spyOn(console, 'info').mockImplementation(() => {});
-    const consoleWarn = jest
-      .spyOn(console, 'warn')
-      .mockImplementation(() => {});
-    const consoleError = jest
-      .spyOn(console, 'error')
-      .mockImplementation(() => {});
-    reportMessage('hey', 'ignore');
-    reportMessage('hey', 'log');
-    reportMessage('hey', 'warn');
-    reportMessage('hey', 'error');
-    expect(() =>
-      reportMessage('hey', 'throw'),
-    ).toThrowErrorMatchingInlineSnapshot(`"hey"`);
-    expect(() =>
-      // @ts-expect-error: for test
-      reportMessage('hey', 'foo'),
-    ).toThrowErrorMatchingInlineSnapshot(
-      `"Unexpected \\"reportingSeverity\\" value: foo."`,
-    );
-    expect(consoleLog).toBeCalledTimes(1);
-    expect(consoleLog).toBeCalledWith(expect.stringMatching(/.*\[INFO].* hey/));
-    expect(consoleWarn).toBeCalledTimes(1);
-    expect(consoleWarn).toBeCalledWith(
-      expect.stringMatching(/.*\[WARNING].* hey/),
-    );
-    expect(consoleError).toBeCalledTimes(1);
-    expect(consoleError).toBeCalledWith(
-      expect.stringMatching(/.*\[ERROR].* hey/),
-    );
-  });
-});
diff --git a/packages/docusaurus-utils/src/__tests__/jsUtils.test.ts b/packages/docusaurus-utils/src/__tests__/jsUtils.test.ts
new file mode 100644
index 0000000000..53bc48469a
--- /dev/null
+++ b/packages/docusaurus-utils/src/__tests__/jsUtils.test.ts
@@ -0,0 +1,189 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {
+  removeSuffix,
+  removePrefix,
+  getElementsAround,
+  mapAsyncSequential,
+  findAsyncSequential,
+  reportMessage,
+} from '../jsUtils';
+import _ from 'lodash';
+
+describe('removeSuffix', () => {
+  test('should no-op 1', () => {
+    expect(removeSuffix('abcdef', 'ijk')).toEqual('abcdef');
+  });
+  test('should no-op 2', () => {
+    expect(removeSuffix('abcdef', 'abc')).toEqual('abcdef');
+  });
+  test('should no-op 3', () => {
+    expect(removeSuffix('abcdef', '')).toEqual('abcdef');
+  });
+  test('should remove suffix', () => {
+    expect(removeSuffix('abcdef', 'ef')).toEqual('abcd');
+  });
+});
+
+describe('removePrefix', () => {
+  test('should no-op 1', () => {
+    expect(removePrefix('abcdef', 'ijk')).toEqual('abcdef');
+  });
+  test('should no-op 2', () => {
+    expect(removePrefix('abcdef', 'def')).toEqual('abcdef');
+  });
+  test('should no-op 3', () => {
+    expect(removePrefix('abcdef', '')).toEqual('abcdef');
+  });
+  test('should remove prefix', () => {
+    expect(removePrefix('abcdef', 'ab')).toEqual('cdef');
+  });
+});
+
+describe('getElementsAround', () => {
+  test('can return elements around', () => {
+    expect(getElementsAround(['a', 'b', 'c', 'd'], 0)).toEqual({
+      previous: undefined,
+      next: 'b',
+    });
+    expect(getElementsAround(['a', 'b', 'c', 'd'], 1)).toEqual({
+      previous: 'a',
+      next: 'c',
+    });
+    expect(getElementsAround(['a', 'b', 'c', 'd'], 2)).toEqual({
+      previous: 'b',
+      next: 'd',
+    });
+    expect(getElementsAround(['a', 'b', 'c', 'd'], 3)).toEqual({
+      previous: 'c',
+      next: undefined,
+    });
+  });
+
+  test('throws if bad index is provided', () => {
+    expect(() =>
+      getElementsAround(['a', 'b', 'c', 'd'], -1),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `"Valid \\"aroundIndex\\" for array (of size 4) are between 0 and 3, but you provided -1."`,
+    );
+    expect(() =>
+      getElementsAround(['a', 'b', 'c', 'd'], 4),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `"Valid \\"aroundIndex\\" for array (of size 4) are between 0 and 3, but you provided 4."`,
+    );
+  });
+});
+
+describe('mapAsyncSequential', () => {
+  function sleep(timeout: number): Promise<void> {
+    return new Promise((resolve) => {
+      setTimeout(resolve, timeout);
+    });
+  }
+
+  test('map sequentially', async () => {
+    const itemToTimeout: Record<string, number> = {
+      '1': 50,
+      '2': 150,
+      '3': 100,
+    };
+    const items = Object.keys(itemToTimeout);
+
+    const itemMapStartsAt: Record<string, number> = {};
+    const itemMapEndsAt: Record<string, number> = {};
+
+    const timeBefore = Date.now();
+    await expect(
+      mapAsyncSequential(items, async (item) => {
+        const itemTimeout = itemToTimeout[item];
+        itemMapStartsAt[item] = Date.now();
+        await sleep(itemTimeout);
+        itemMapEndsAt[item] = Date.now();
+        return `${item} mapped`;
+      }),
+    ).resolves.toEqual(['1 mapped', '2 mapped', '3 mapped']);
+    const timeAfter = Date.now();
+
+    const timeTotal = timeAfter - timeBefore;
+
+    const totalTimeouts = _.sum(Object.values(itemToTimeout));
+    expect(timeTotal).toBeGreaterThanOrEqual(totalTimeouts - 20);
+
+    expect(itemMapStartsAt['1']).toBeGreaterThanOrEqual(0);
+    expect(itemMapStartsAt['2']).toBeGreaterThanOrEqual(
+      itemMapEndsAt['1'] - 20,
+    );
+    expect(itemMapStartsAt['3']).toBeGreaterThanOrEqual(
+      itemMapEndsAt['2'] - 20,
+    );
+  });
+});
+
+describe('findAsyncSequential', () => {
+  function sleep(timeout: number): Promise<void> {
+    return new Promise((resolve) => {
+      setTimeout(resolve, timeout);
+    });
+  }
+
+  test('find sequentially', async () => {
+    const items = ['1', '2', '3'];
+
+    const findFn = jest.fn(async (item: string) => {
+      await sleep(50);
+      return item === '2';
+    });
+
+    const timeBefore = Date.now();
+    await expect(findAsyncSequential(items, findFn)).resolves.toEqual('2');
+    const timeAfter = Date.now();
+
+    expect(findFn).toHaveBeenCalledTimes(2);
+    expect(findFn).toHaveBeenNthCalledWith(1, '1');
+    expect(findFn).toHaveBeenNthCalledWith(2, '2');
+
+    const timeTotal = timeAfter - timeBefore;
+    expect(timeTotal).toBeGreaterThanOrEqual(80);
+    expect(timeTotal).toBeLessThan(120);
+  });
+});
+
+describe('reportMessage', () => {
+  test('all severities', () => {
+    const consoleLog = jest.spyOn(console, 'info').mockImplementation(() => {});
+    const consoleWarn = jest
+      .spyOn(console, 'warn')
+      .mockImplementation(() => {});
+    const consoleError = jest
+      .spyOn(console, 'error')
+      .mockImplementation(() => {});
+    reportMessage('hey', 'ignore');
+    reportMessage('hey', 'log');
+    reportMessage('hey', 'warn');
+    reportMessage('hey', 'error');
+    expect(() =>
+      reportMessage('hey', 'throw'),
+    ).toThrowErrorMatchingInlineSnapshot(`"hey"`);
+    expect(() =>
+      // @ts-expect-error: for test
+      reportMessage('hey', 'foo'),
+    ).toThrowErrorMatchingInlineSnapshot(
+      `"Unexpected \\"reportingSeverity\\" value: foo."`,
+    );
+    expect(consoleLog).toBeCalledTimes(1);
+    expect(consoleLog).toBeCalledWith(expect.stringMatching(/.*\[INFO].* hey/));
+    expect(consoleWarn).toBeCalledTimes(1);
+    expect(consoleWarn).toBeCalledWith(
+      expect.stringMatching(/.*\[WARNING].* hey/),
+    );
+    expect(consoleError).toBeCalledTimes(1);
+    expect(consoleError).toBeCalledWith(
+      expect.stringMatching(/.*\[ERROR].* hey/),
+    );
+  });
+});
diff --git a/packages/docusaurus-utils/src/__tests__/pathUtils.test.ts b/packages/docusaurus-utils/src/__tests__/pathUtils.test.ts
index 0c3666d137..96089fa13a 100644
--- a/packages/docusaurus-utils/src/__tests__/pathUtils.test.ts
+++ b/packages/docusaurus-utils/src/__tests__/pathUtils.test.ts
@@ -12,6 +12,7 @@ import {
   posixPath,
   aliasedSitePath,
   toMessageRelativeFilePath,
+  addTrailingPathSeparator,
 } from '../pathUtils';
 import path from 'path';
 
@@ -116,63 +117,63 @@ describe('shortName', () => {
   });
 });
 
-describe('toMessageRelativeFilePath', () => {
-  test('behaves correctly', () => {
-    jest
-      .spyOn(process, 'cwd')
-      .mockImplementationOnce(() => path.join(__dirname, '..'));
-    expect(
-      toMessageRelativeFilePath(path.join(__dirname, 'foo/bar.js')),
-    ).toEqual('__tests__/foo/bar.js');
+test('toMessageRelativeFilePath', () => {
+  jest
+    .spyOn(process, 'cwd')
+    .mockImplementationOnce(() => path.join(__dirname, '..'));
+  expect(toMessageRelativeFilePath(path.join(__dirname, 'foo/bar.js'))).toEqual(
+    '__tests__/foo/bar.js',
+  );
+});
+
+test('escapePath', () => {
+  const asserts: Record<string, string> = {
+    'c:/aaaa\\bbbb': 'c:/aaaa\\\\bbbb',
+    'c:\\aaaa\\bbbb\\★': 'c:\\\\aaaa\\\\bbbb\\\\★',
+    '\\\\?\\c:\\aaaa\\bbbb': '\\\\\\\\?\\\\c:\\\\aaaa\\\\bbbb',
+    'c:\\aaaa\\bbbb': 'c:\\\\aaaa\\\\bbbb',
+    'foo\\bar': 'foo\\\\bar',
+    'foo\\bar/lol': 'foo\\\\bar/lol',
+    'website\\docs/**/*.{md,mdx}': 'website\\\\docs/**/*.{md,mdx}',
+  };
+  Object.keys(asserts).forEach((file) => {
+    expect(escapePath(file)).toBe(asserts[file]);
   });
 });
 
-describe('escapePath', () => {
-  test('escapePath works', () => {
-    const asserts: Record<string, string> = {
-      'c:/aaaa\\bbbb': 'c:/aaaa\\\\bbbb',
-      'c:\\aaaa\\bbbb\\★': 'c:\\\\aaaa\\\\bbbb\\\\★',
-      '\\\\?\\c:\\aaaa\\bbbb': '\\\\\\\\?\\\\c:\\\\aaaa\\\\bbbb',
-      'c:\\aaaa\\bbbb': 'c:\\\\aaaa\\\\bbbb',
-      'foo\\bar': 'foo\\\\bar',
-      'foo\\bar/lol': 'foo\\\\bar/lol',
-      'website\\docs/**/*.{md,mdx}': 'website\\\\docs/**/*.{md,mdx}',
-    };
-    Object.keys(asserts).forEach((file) => {
-      expect(escapePath(file)).toBe(asserts[file]);
-    });
+test('posixPath', () => {
+  const asserts: Record<string, string> = {
+    'c:/aaaa\\bbbb': 'c:/aaaa/bbbb',
+    'c:\\aaaa\\bbbb\\★': 'c:\\aaaa\\bbbb\\★',
+    '\\\\?\\c:\\aaaa\\bbbb': '\\\\?\\c:\\aaaa\\bbbb',
+    'c:\\aaaa\\bbbb': 'c:/aaaa/bbbb',
+    'foo\\bar': 'foo/bar',
+    'foo\\bar/lol': 'foo/bar/lol',
+    'website\\docs/**/*.{md,mdx}': 'website/docs/**/*.{md,mdx}',
+  };
+  Object.keys(asserts).forEach((file) => {
+    expect(posixPath(file)).toBe(asserts[file]);
   });
 });
 
-describe('posixPath', () => {
-  test('posixPath works', () => {
-    const asserts: Record<string, string> = {
-      'c:/aaaa\\bbbb': 'c:/aaaa/bbbb',
-      'c:\\aaaa\\bbbb\\★': 'c:\\aaaa\\bbbb\\★',
-      '\\\\?\\c:\\aaaa\\bbbb': '\\\\?\\c:\\aaaa\\bbbb',
-      'c:\\aaaa\\bbbb': 'c:/aaaa/bbbb',
-      'foo\\bar': 'foo/bar',
-      'foo\\bar/lol': 'foo/bar/lol',
-      'website\\docs/**/*.{md,mdx}': 'website/docs/**/*.{md,mdx}',
-    };
-    Object.keys(asserts).forEach((file) => {
-      expect(posixPath(file)).toBe(asserts[file]);
-    });
+test('aliasedSitePath', () => {
+  const asserts: Record<string, string> = {
+    'user/website/docs/asd.md': '@site/docs/asd.md',
+    'user/website/versioned_docs/foo/bar.md': '@site/versioned_docs/foo/bar.md',
+    'user/docs/test.md': '@site/../docs/test.md',
+  };
+  Object.keys(asserts).forEach((file) => {
+    expect(posixPath(aliasedSitePath(file, 'user/website'))).toBe(
+      asserts[file],
+    );
   });
 });
 
-describe('aliasedSitePath', () => {
-  test('behaves correctly', () => {
-    const asserts: Record<string, string> = {
-      'user/website/docs/asd.md': '@site/docs/asd.md',
-      'user/website/versioned_docs/foo/bar.md':
-        '@site/versioned_docs/foo/bar.md',
-      'user/docs/test.md': '@site/../docs/test.md',
-    };
-    Object.keys(asserts).forEach((file) => {
-      expect(posixPath(aliasedSitePath(file, 'user/website'))).toBe(
-        asserts[file],
-      );
-    });
-  });
+test('addTrailingPathSeparator', () => {
+  expect(addTrailingPathSeparator('foo')).toEqual(
+    process.platform === 'win32' ? 'foo\\' : 'foo/',
+  );
+  expect(addTrailingPathSeparator('foo/')).toEqual(
+    process.platform === 'win32' ? 'foo\\' : 'foo/',
+  );
 });
diff --git a/packages/docusaurus-utils/src/__tests__/urlUtils.test.ts b/packages/docusaurus-utils/src/__tests__/urlUtils.test.ts
index 3acd892bbe..22410a8e76 100644
--- a/packages/docusaurus-utils/src/__tests__/urlUtils.test.ts
+++ b/packages/docusaurus-utils/src/__tests__/urlUtils.test.ts
@@ -5,7 +5,17 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {normalizeUrl, getEditUrl} from '../urlUtils';
+import {
+  normalizeUrl,
+  getEditUrl,
+  fileToPath,
+  isValidPathname,
+  addTrailingSlash,
+  addLeadingSlash,
+  removeTrailingSlash,
+  resolvePathname,
+  encodePath,
+} from '../urlUtils';
 
 describe('normalizeUrl', () => {
   test('should normalize urls correctly', () => {
@@ -150,3 +160,82 @@ describe('getEditUrl', () => {
     expect(getEditUrl('foo/bar.md')).toBeUndefined();
   });
 });
+
+test('fileToPath', () => {
+  const asserts: Record<string, string> = {
+    'index.md': '/',
+    'hello/index.md': '/hello/',
+    'foo.md': '/foo',
+    'foo/bar.md': '/foo/bar',
+    'index.js': '/',
+    'hello/index.js': '/hello/',
+    'foo.js': '/foo',
+    'foo/bar.js': '/foo/bar',
+  };
+  Object.keys(asserts).forEach((file) => {
+    expect(fileToPath(file)).toBe(asserts[file]);
+  });
+});
+
+test('isValidPathname', () => {
+  expect(isValidPathname('/')).toBe(true);
+  expect(isValidPathname('/hey')).toBe(true);
+  expect(isValidPathname('/hey/ho')).toBe(true);
+  expect(isValidPathname('/hey/ho/')).toBe(true);
+  expect(isValidPathname('/hey/h%C3%B4/')).toBe(true);
+  expect(isValidPathname('/hey///ho///')).toBe(true); // Unexpected but valid
+  expect(isValidPathname('/hey/héllô you')).toBe(true);
+
+  expect(isValidPathname('')).toBe(false);
+  expect(isValidPathname('hey')).toBe(false);
+  expect(isValidPathname('/hey?qs=ho')).toBe(false);
+  expect(isValidPathname('https://fb.com/hey')).toBe(false);
+  expect(isValidPathname('//hey')).toBe(false);
+  expect(isValidPathname('////')).toBe(false);
+});
+
+describe('addTrailingSlash', () => {
+  test('should no-op', () => {
+    expect(addTrailingSlash('/abcd/')).toEqual('/abcd/');
+  });
+  test('should add /', () => {
+    expect(addTrailingSlash('/abcd')).toEqual('/abcd/');
+  });
+});
+
+describe('addLeadingSlash', () => {
+  test('should no-op', () => {
+    expect(addLeadingSlash('/abc')).toEqual('/abc');
+  });
+  test('should add /', () => {
+    expect(addLeadingSlash('abc')).toEqual('/abc');
+  });
+});
+
+describe('removeTrailingSlash', () => {
+  test('should no-op', () => {
+    expect(removeTrailingSlash('/abcd')).toEqual('/abcd');
+  });
+  test('should remove /', () => {
+    expect(removeTrailingSlash('/abcd/')).toEqual('/abcd');
+  });
+});
+
+test('resolvePathname', () => {
+  // These tests are directly copied from https://github.com/mjackson/resolve-pathname/blob/master/modules/__tests__/resolvePathname-test.js
+  // Maybe we want to wrap that logic in the future?
+  expect(resolvePathname('c')).toEqual('c');
+  expect(resolvePathname('c', 'a/b')).toEqual('a/c');
+  expect(resolvePathname('/c', '/a/b')).toEqual('/c');
+  expect(resolvePathname('', '/a/b')).toEqual('/a/b');
+  expect(resolvePathname('../c', '/a/b')).toEqual('/c');
+  expect(resolvePathname('c', '/a/b')).toEqual('/a/c');
+  expect(resolvePathname('c', '/a/')).toEqual('/a/c');
+  expect(resolvePathname('..', '/a/b')).toEqual('/');
+});
+
+test('encodePath', () => {
+  expect(encodePath('a/foo/')).toEqual('a/foo/');
+  expect(encodePath('a/<foo>/')).toEqual('a/%3Cfoo%3E/');
+  expect(encodePath('a/你好/')).toEqual('a/%E4%BD%A0%E5%A5%BD/');
+});
diff --git a/packages/docusaurus-utils/src/emitUtils.ts b/packages/docusaurus-utils/src/emitUtils.ts
new file mode 100644
index 0000000000..bb71a99f48
--- /dev/null
+++ b/packages/docusaurus-utils/src/emitUtils.ts
@@ -0,0 +1,113 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import path from 'path';
+import fs from 'fs-extra';
+import {createHash} from 'crypto';
+import {simpleHash, docuHash} from './hashUtils';
+import {findAsyncSequential} from './jsUtils';
+
+const fileHash = new Map<string, string>();
+
+export async function generate(
+  generatedFilesDir: string,
+  file: string,
+  content: string,
+  skipCache: boolean = process.env.NODE_ENV === 'production',
+): Promise<void> {
+  const filepath = path.join(generatedFilesDir, file);
+
+  if (skipCache) {
+    await fs.ensureDir(path.dirname(filepath));
+    await fs.writeFile(filepath, content);
+    return;
+  }
+
+  let lastHash = fileHash.get(filepath);
+
+  // If file already exists but its not in runtime cache yet,
+  // we try to calculate the content hash and then compare
+  // This is to avoid unnecessary overwriting and we can reuse old file.
+  if (!lastHash && (await fs.pathExists(filepath))) {
+    const lastContent = await fs.readFile(filepath, 'utf8');
+    lastHash = createHash('md5').update(lastContent).digest('hex');
+    fileHash.set(filepath, lastHash);
+  }
+
+  const currentHash = createHash('md5').update(content).digest('hex');
+
+  if (lastHash !== currentHash) {
+    await fs.ensureDir(path.dirname(filepath));
+    await fs.writeFile(filepath, content);
+    fileHash.set(filepath, currentHash);
+  }
+}
+
+const chunkNameCache = new Map();
+
+/**
+ * Generate unique chunk name given a module path.
+ */
+export function genChunkName(
+  modulePath: string,
+  prefix?: string,
+  preferredName?: string,
+  shortId: boolean = process.env.NODE_ENV === 'production',
+): string {
+  let chunkName: string | undefined = chunkNameCache.get(modulePath);
+  if (!chunkName) {
+    if (shortId) {
+      chunkName = simpleHash(modulePath, 8);
+    } else {
+      let str = modulePath;
+      if (preferredName) {
+        const shortHash = simpleHash(modulePath, 3);
+        str = `${preferredName}${shortHash}`;
+      }
+      const name = str === '/' ? 'index' : docuHash(str);
+      chunkName = prefix ? `${prefix}---${name}` : name;
+    }
+    chunkNameCache.set(modulePath, chunkName);
+  }
+  return chunkName;
+}
+
+/**
+ * @param permalink The URL that the HTML file corresponds to, without base URL
+ * @param outDir Full path to the output directory
+ * @param trailingSlash The site config option. If provided, only one path will
+ * be read.
+ * @returns This returns a buffer, which you have to decode string yourself if
+ * needed. (Not always necessary since the output isn't for human consumption
+ * anyways, and most HTML manipulation libs accept buffers)
+ */
+export async function readOutputHTMLFile(
+  permalink: string,
+  outDir: string,
+  trailingSlash: boolean | undefined,
+): Promise<Buffer> {
+  const withTrailingSlashPath = path.join(outDir, permalink, 'index.html');
+  const withoutTrailingSlashPath = path.join(
+    outDir,
+    `${permalink.replace(/\/$/, '')}.html`,
+  );
+  if (trailingSlash) {
+    return fs.readFile(withTrailingSlashPath);
+  } else if (trailingSlash === false) {
+    return fs.readFile(withoutTrailingSlashPath);
+  }
+  const HTMLPath = await findAsyncSequential(
+    [withTrailingSlashPath, withoutTrailingSlashPath],
+    fs.pathExists,
+  );
+  if (!HTMLPath) {
+    throw new Error(
+      `Expected output HTML file to be found at ${withTrailingSlashPath}`,
+    );
+  }
+  return fs.readFile(HTMLPath);
+}
diff --git a/packages/docusaurus-utils/src/i18nUtils.ts b/packages/docusaurus-utils/src/i18nUtils.ts
new file mode 100644
index 0000000000..3e3005fcfe
--- /dev/null
+++ b/packages/docusaurus-utils/src/i18nUtils.ts
@@ -0,0 +1,58 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import path from 'path';
+import _ from 'lodash';
+import type {TranslationFileContent, TranslationFile} from '@docusaurus/types';
+import {DEFAULT_PLUGIN_ID} from './constants';
+
+export function mergeTranslations(
+  contents: TranslationFileContent[],
+): TranslationFileContent {
+  return contents.reduce((acc, content) => ({...acc, ...content}), {});
+}
+
+// Useful to update all the messages of a translation file
+// Used in tests to simulate translations
+export function updateTranslationFileMessages(
+  translationFile: TranslationFile,
+  updateMessage: (message: string) => string,
+): TranslationFile {
+  return {
+    ...translationFile,
+    content: _.mapValues(translationFile.content, (translation) => ({
+      ...translation,
+      message: updateMessage(translation.message),
+    })),
+  };
+}
+
+export function getPluginI18nPath({
+  siteDir,
+  locale,
+  pluginName,
+  pluginId = DEFAULT_PLUGIN_ID,
+  subPaths = [],
+}: {
+  siteDir: string;
+  locale: string;
+  pluginName: string;
+  pluginId?: string | undefined;
+  subPaths?: string[];
+}): string {
+  return path.join(
+    siteDir,
+    'i18n',
+    // namespace first by locale: convenient to work in a single folder for a
+    // translator
+    locale,
+    // Make it convenient to use for single-instance
+    // ie: return "docs", not "docs-default" nor "docs/default"
+    `${pluginName}${pluginId === DEFAULT_PLUGIN_ID ? '' : `-${pluginId}`}`,
+    ...subPaths,
+  );
+}
diff --git a/packages/docusaurus-utils/src/index.ts b/packages/docusaurus-utils/src/index.ts
index fdb3f6087d..9c66f3a9f4 100644
--- a/packages/docusaurus-utils/src/index.ts
+++ b/packages/docusaurus-utils/src/index.ts
@@ -5,23 +5,6 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import logger from '@docusaurus/logger';
-import path from 'path';
-import {createHash} from 'crypto';
-import _ from 'lodash';
-import fs from 'fs-extra';
-import {URL} from 'url';
-import type {
-  ReportingSeverity,
-  TranslationFileContent,
-  TranslationFile,
-} from '@docusaurus/types';
-
-import resolvePathnameUnsafe from 'resolve-pathname';
-
-import {simpleHash, docuHash} from './hashUtils';
-import {DEFAULT_PLUGIN_ID} from './constants';
-
 export {
   NODE_MAJOR_VERSION,
   NODE_MINOR_VERSION,
@@ -37,8 +20,32 @@ export {
   DEFAULT_PLUGIN_ID,
   WEBPACK_URL_LOADER_LIMIT,
 } from './constants';
+export {generate, genChunkName, readOutputHTMLFile} from './emitUtils';
 export {getFileCommitDate, GitNotFoundError} from './gitUtils';
-export {normalizeUrl, getEditUrl} from './urlUtils';
+export {
+  mergeTranslations,
+  updateTranslationFileMessages,
+  getPluginI18nPath,
+} from './i18nUtils';
+export {
+  removeSuffix,
+  removePrefix,
+  getElementsAround,
+  mapAsyncSequential,
+  findAsyncSequential,
+  reportMessage,
+} from './jsUtils';
+export {
+  normalizeUrl,
+  getEditUrl,
+  fileToPath,
+  encodePath,
+  isValidPathname,
+  resolvePathname,
+  addLeadingSlash,
+  addTrailingSlash,
+  removeTrailingSlash,
+} from './urlUtils';
 export {
   type Tag,
   type FrontMatterTag,
@@ -69,6 +76,7 @@ export {
   toMessageRelativeFilePath,
   aliasedSitePath,
   escapePath,
+  addTrailingPathSeparator,
 } from './pathUtils';
 export {md5Hash, simpleHash, docuHash} from './hashUtils';
 export {
@@ -85,285 +93,3 @@ export {
   findFolderContainingFile,
   getFolderContainingFile,
 } from './dataFileUtils';
-
-const fileHash = new Map<string, string>();
-export async function generate(
-  generatedFilesDir: string,
-  file: string,
-  content: string,
-  skipCache: boolean = process.env.NODE_ENV === 'production',
-): Promise<void> {
-  const filepath = path.join(generatedFilesDir, file);
-
-  if (skipCache) {
-    await fs.ensureDir(path.dirname(filepath));
-    await fs.writeFile(filepath, content);
-    return;
-  }
-
-  let lastHash = fileHash.get(filepath);
-
-  // If file already exists but its not in runtime cache yet,
-  // we try to calculate the content hash and then compare
-  // This is to avoid unnecessary overwriting and we can reuse old file.
-  if (!lastHash && (await fs.pathExists(filepath))) {
-    const lastContent = await fs.readFile(filepath, 'utf8');
-    lastHash = createHash('md5').update(lastContent).digest('hex');
-    fileHash.set(filepath, lastHash);
-  }
-
-  const currentHash = createHash('md5').update(content).digest('hex');
-
-  if (lastHash !== currentHash) {
-    await fs.ensureDir(path.dirname(filepath));
-    await fs.writeFile(filepath, content);
-    fileHash.set(filepath, currentHash);
-  }
-}
-
-const indexRE = /(?<dirname>^|.*\/)index\.(?:mdx?|jsx?|tsx?)$/i;
-const extRE = /\.(?:mdx?|jsx?|tsx?)$/;
-
-/**
- * Convert filepath to url path.
- * Example: 'index.md' -> '/', 'foo/bar.js' -> '/foo/bar',
- */
-export function fileToPath(file: string): string {
-  if (indexRE.test(file)) {
-    return file.replace(indexRE, '/$1');
-  }
-  return `/${file.replace(extRE, '').replace(/\\/g, '/')}`;
-}
-
-export function encodePath(userPath: string): string {
-  return userPath
-    .split('/')
-    .map((item) => encodeURIComponent(item))
-    .join('/');
-}
-
-const chunkNameCache = new Map();
-/**
- * Generate unique chunk name given a module path.
- */
-export function genChunkName(
-  modulePath: string,
-  prefix?: string,
-  preferredName?: string,
-  shortId: boolean = process.env.NODE_ENV === 'production',
-): string {
-  let chunkName: string | undefined = chunkNameCache.get(modulePath);
-  if (!chunkName) {
-    if (shortId) {
-      chunkName = simpleHash(modulePath, 8);
-    } else {
-      let str = modulePath;
-      if (preferredName) {
-        const shortHash = simpleHash(modulePath, 3);
-        str = `${preferredName}${shortHash}`;
-      }
-      const name = str === '/' ? 'index' : docuHash(str);
-      chunkName = prefix ? `${prefix}---${name}` : name;
-    }
-    chunkNameCache.set(modulePath, chunkName);
-  }
-  return chunkName;
-}
-
-export function isValidPathname(str: string): boolean {
-  if (!str.startsWith('/')) {
-    return false;
-  }
-  try {
-    // weird, but is there a better way?
-    const parsedPathname = new URL(str, 'https://domain.com').pathname;
-    return parsedPathname === str || parsedPathname === encodeURI(str);
-  } catch {
-    return false;
-  }
-}
-
-// resolve pathname and fail fast if resolution fails
-export function resolvePathname(to: string, from?: string): string {
-  return resolvePathnameUnsafe(to, from);
-}
-export function addLeadingSlash(str: string): string {
-  return str.startsWith('/') ? str : `/${str}`;
-}
-
-export function addTrailingPathSeparator(str: string): string {
-  return str.endsWith(path.sep)
-    ? str
-    : // If this is Windows, we need to change the forward slash to backward
-      `${str.replace(/\/$/, '')}${path.sep}`;
-}
-
-// TODO deduplicate: also present in @docusaurus/utils-common
-export function addTrailingSlash(str: string): string {
-  return str.endsWith('/') ? str : `${str}/`;
-}
-export function removeTrailingSlash(str: string): string {
-  return removeSuffix(str, '/');
-}
-
-export function removeSuffix(str: string, suffix: string): string {
-  if (suffix === '') {
-    return str; // always returns "" otherwise!
-  }
-  return str.endsWith(suffix) ? str.slice(0, -suffix.length) : str;
-}
-
-export function removePrefix(str: string, prefix: string): string {
-  return str.startsWith(prefix) ? str.slice(prefix.length) : str;
-}
-
-export function getElementsAround<T>(
-  array: T[],
-  aroundIndex: number,
-): {
-  next: T | undefined;
-  previous: T | undefined;
-} {
-  const min = 0;
-  const max = array.length - 1;
-  if (aroundIndex < min || aroundIndex > max) {
-    throw new Error(
-      `Valid "aroundIndex" for array (of size ${array.length}) are between ${min} and ${max}, but you provided ${aroundIndex}.`,
-    );
-  }
-  const previous = aroundIndex === min ? undefined : array[aroundIndex - 1];
-  const next = aroundIndex === max ? undefined : array[aroundIndex + 1];
-  return {previous, next};
-}
-
-export function getPluginI18nPath({
-  siteDir,
-  locale,
-  pluginName,
-  pluginId = DEFAULT_PLUGIN_ID,
-  subPaths = [],
-}: {
-  siteDir: string;
-  locale: string;
-  pluginName: string;
-  pluginId?: string | undefined;
-  subPaths?: string[];
-}): string {
-  return path.join(
-    siteDir,
-    'i18n',
-    // namespace first by locale: convenient to work in a single folder for a
-    // translator
-    locale,
-    // Make it convenient to use for single-instance
-    // ie: return "docs", not "docs-default" nor "docs/default"
-    `${pluginName}${pluginId === DEFAULT_PLUGIN_ID ? '' : `-${pluginId}`}`,
-    ...subPaths,
-  );
-}
-
-/**
- * @param permalink The URL that the HTML file corresponds to, without base URL
- * @param outDir Full path to the output directory
- * @param trailingSlash The site config option. If provided, only one path will
- * be read.
- * @returns This returns a buffer, which you have to decode string yourself if
- * needed. (Not always necessary since the output isn't for human consumption
- * anyways, and most HTML manipulation libs accept buffers)
- */
-export async function readOutputHTMLFile(
-  permalink: string,
-  outDir: string,
-  trailingSlash: boolean | undefined,
-): Promise<Buffer> {
-  const withTrailingSlashPath = path.join(outDir, permalink, 'index.html');
-  const withoutTrailingSlashPath = path.join(
-    outDir,
-    `${permalink.replace(/\/$/, '')}.html`,
-  );
-  if (trailingSlash) {
-    return fs.readFile(withTrailingSlashPath);
-  } else if (trailingSlash === false) {
-    return fs.readFile(withoutTrailingSlashPath);
-  }
-  const HTMLPath = await findAsyncSequential(
-    [withTrailingSlashPath, withoutTrailingSlashPath],
-    fs.pathExists,
-  );
-  if (!HTMLPath) {
-    throw new Error(
-      `Expected output HTML file to be found at ${withTrailingSlashPath}`,
-    );
-  }
-  return fs.readFile(HTMLPath);
-}
-
-export async function mapAsyncSequential<T, R>(
-  array: T[],
-  action: (t: T) => Promise<R>,
-): Promise<R[]> {
-  const results: R[] = [];
-  for (const t of array) {
-    const result = await action(t);
-    results.push(result);
-  }
-  return results;
-}
-
-export async function findAsyncSequential<T>(
-  array: T[],
-  predicate: (t: T) => Promise<boolean>,
-): Promise<T | undefined> {
-  for (const t of array) {
-    if (await predicate(t)) {
-      return t;
-    }
-  }
-  return undefined;
-}
-
-export function reportMessage(
-  message: string,
-  reportingSeverity: ReportingSeverity,
-): void {
-  switch (reportingSeverity) {
-    case 'ignore':
-      break;
-    case 'log':
-      logger.info(message);
-      break;
-    case 'warn':
-      logger.warn(message);
-      break;
-    case 'error':
-      logger.error(message);
-      break;
-    case 'throw':
-      throw new Error(message);
-    default:
-      throw new Error(
-        `Unexpected "reportingSeverity" value: ${reportingSeverity}.`,
-      );
-  }
-}
-
-export function mergeTranslations(
-  contents: TranslationFileContent[],
-): TranslationFileContent {
-  return contents.reduce((acc, content) => ({...acc, ...content}), {});
-}
-
-// Useful to update all the messages of a translation file
-// Used in tests to simulate translations
-export function updateTranslationFileMessages(
-  translationFile: TranslationFile,
-  updateMessage: (message: string) => string,
-): TranslationFile {
-  return {
-    ...translationFile,
-    content: _.mapValues(translationFile.content, (translation) => ({
-      ...translation,
-      message: updateMessage(translation.message),
-    })),
-  };
-}
diff --git a/packages/docusaurus-utils/src/jsUtils.ts b/packages/docusaurus-utils/src/jsUtils.ts
new file mode 100644
index 0000000000..a0db09b3d1
--- /dev/null
+++ b/packages/docusaurus-utils/src/jsUtils.ts
@@ -0,0 +1,88 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import type {ReportingSeverity} from '@docusaurus/types';
+import logger from '@docusaurus/logger';
+
+export function removeSuffix(str: string, suffix: string): string {
+  if (suffix === '') {
+    return str; // always returns "" otherwise!
+  }
+  return str.endsWith(suffix) ? str.slice(0, -suffix.length) : str;
+}
+
+export function removePrefix(str: string, prefix: string): string {
+  return str.startsWith(prefix) ? str.slice(prefix.length) : str;
+}
+
+export function getElementsAround<T>(
+  array: T[],
+  aroundIndex: number,
+): {
+  next: T | undefined;
+  previous: T | undefined;
+} {
+  const min = 0;
+  const max = array.length - 1;
+  if (aroundIndex < min || aroundIndex > max) {
+    throw new Error(
+      `Valid "aroundIndex" for array (of size ${array.length}) are between ${min} and ${max}, but you provided ${aroundIndex}.`,
+    );
+  }
+  const previous = aroundIndex === min ? undefined : array[aroundIndex - 1];
+  const next = aroundIndex === max ? undefined : array[aroundIndex + 1];
+  return {previous, next};
+}
+
+export async function mapAsyncSequential<T, R>(
+  array: T[],
+  action: (t: T) => Promise<R>,
+): Promise<R[]> {
+  const results: R[] = [];
+  for (const t of array) {
+    const result = await action(t);
+    results.push(result);
+  }
+  return results;
+}
+
+export async function findAsyncSequential<T>(
+  array: T[],
+  predicate: (t: T) => Promise<boolean>,
+): Promise<T | undefined> {
+  for (const t of array) {
+    if (await predicate(t)) {
+      return t;
+    }
+  }
+  return undefined;
+}
+
+export function reportMessage(
+  message: string,
+  reportingSeverity: ReportingSeverity,
+): void {
+  switch (reportingSeverity) {
+    case 'ignore':
+      break;
+    case 'log':
+      logger.info(message);
+      break;
+    case 'warn':
+      logger.warn(message);
+      break;
+    case 'error':
+      logger.error(message);
+      break;
+    case 'throw':
+      throw new Error(message);
+    default:
+      throw new Error(
+        `Unexpected "reportingSeverity" value: ${reportingSeverity}.`,
+      );
+  }
+}
diff --git a/packages/docusaurus-utils/src/pathUtils.ts b/packages/docusaurus-utils/src/pathUtils.ts
index 384b73a2be..db005eab56 100644
--- a/packages/docusaurus-utils/src/pathUtils.ts
+++ b/packages/docusaurus-utils/src/pathUtils.ts
@@ -5,10 +5,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-// Based on https://github.com/gatsbyjs/gatsby/pull/21518/files
-
 import path from 'path';
 
+// Based on https://github.com/gatsbyjs/gatsby/pull/21518/files
 // MacOS (APFS) and Windows (NTFS) filename length limit = 255 chars,
 // Others = 255 bytes
 const MAX_PATH_SEGMENT_CHARS = 255;
@@ -113,3 +112,10 @@ export function escapePath(str: string): string {
   // Remove the " around the json string;
   return escaped.substring(1, escaped.length - 1);
 }
+
+export function addTrailingPathSeparator(str: string): string {
+  return str.endsWith(path.sep)
+    ? str
+    : // If this is Windows, we need to change the forward slash to backward
+      `${str.replace(/\/$/, '')}${path.sep}`;
+}
diff --git a/packages/docusaurus-utils/src/urlUtils.ts b/packages/docusaurus-utils/src/urlUtils.ts
index 36417158fe..9a69596651 100644
--- a/packages/docusaurus-utils/src/urlUtils.ts
+++ b/packages/docusaurus-utils/src/urlUtils.ts
@@ -5,6 +5,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import {removeSuffix} from './jsUtils';
+import resolvePathnameUnsafe from 'resolve-pathname';
+
 export function normalizeUrl(rawUrls: string[]): string {
   const urls = [...rawUrls];
   const resultArray = [];
@@ -94,3 +97,53 @@ export function getEditUrl(
       normalizeUrl([editUrl, fileRelativePath.replace(/\\/g, '/')])
     : undefined;
 }
+
+/**
+ * Convert filepath to url path.
+ * Example: 'index.md' -> '/', 'foo/bar.js' -> '/foo/bar',
+ */
+export function fileToPath(file: string): string {
+  const indexRE = /(?<dirname>^|.*\/)index\.(?:mdx?|jsx?|tsx?)$/i;
+  const extRE = /\.(?:mdx?|jsx?|tsx?)$/;
+
+  if (indexRE.test(file)) {
+    return file.replace(indexRE, '/$1');
+  }
+  return `/${file.replace(extRE, '').replace(/\\/g, '/')}`;
+}
+
+export function encodePath(userPath: string): string {
+  return userPath
+    .split('/')
+    .map((item) => encodeURIComponent(item))
+    .join('/');
+}
+
+export function isValidPathname(str: string): boolean {
+  if (!str.startsWith('/')) {
+    return false;
+  }
+  try {
+    // weird, but is there a better way?
+    const parsedPathname = new URL(str, 'https://domain.com').pathname;
+    return parsedPathname === str || parsedPathname === encodeURI(str);
+  } catch {
+    return false;
+  }
+}
+
+// resolve pathname and fail fast if resolution fails
+export function resolvePathname(to: string, from?: string): string {
+  return resolvePathnameUnsafe(to, from);
+}
+export function addLeadingSlash(str: string): string {
+  return str.startsWith('/') ? str : `/${str}`;
+}
+
+// TODO deduplicate: also present in @docusaurus/utils-common
+export function addTrailingSlash(str: string): string {
+  return str.endsWith('/') ? str : `${str}/`;
+}
+export function removeTrailingSlash(str: string): string {
+  return removeSuffix(str, '/');
+}