chore(agnostic): Migrate DOMWorld (#6054)

DOMWorld only needs to use Node's `fs` module if you're adding a
filepath as a script/style tag. We can detect this case and run the
`require` inline such that in a browser this code won't execute.

src/common/DOMWorld.ts

@@ -14,7 +14,6 @@
  * limitations under the License.
  */
 
-import * as fs from 'fs';
 import { assert } from './assert';
 import { helper } from './helper';
 import { LifecycleWatcher, PuppeteerLifeCycleEvent } from './LifecycleWatcher';
@@ -25,13 +24,12 @@ import { TimeoutSettings } from './TimeoutSettings';
 import { MouseButtonInput } from './Input';
 import { FrameManager, Frame } from './FrameManager';
 import { getQueryHandlerAndSelector, QueryHandler } from './QueryHandler';
+import { isNode } from '../environment';
 
 // This predicateQueryHandler is declared here so that TypeScript knows about it
 // when it is used in the predicate function below.
 declare const predicateQueryHandler: QueryHandler;
 
-const readFileAsync = helper.promisify(fs.readFile);
-
 export interface WaitForSelectorOptions {
   visible?: boolean;
   hidden?: boolean;
@@ -232,8 +230,15 @@ export class DOMWorld {
   }
 
   /**
-   * @param {!{url?: string, path?: string, content?: string, type?: string}} options
+   * Adds a script tag into the current context.
-   * @returns {!Promise<!ElementHandle>}
+   *
+   * @remarks
+   *
+   * You can pass a URL, filepath or string of contents. Note that when running Puppeteer
+   * in a browser environment you cannot pass a filepath and should use either
+   * `url` or `content`.
+   *
+   * @param options
    */
   async addScriptTag(options: {
     url?: string;
@@ -254,6 +259,14 @@ export class DOMWorld {
     }
 
     if (path !== null) {
+      if (!isNode) {
+        throw new Error(
+          'Cannot pass a filepath to addScriptTag in the browser environment.'
+        );
+      }
+      // eslint-disable-next-line @typescript-eslint/no-var-requires
+      const fs = require('fs');
+      const readFileAsync = helper.promisify(fs.readFile);
       let contents = await readFileAsync(path, 'utf8');
       contents += '//# sourceURL=' + path.replace(/\n/g, '');
       const context = await this.executionContext();
@@ -304,6 +317,17 @@ export class DOMWorld {
     }
   }
 
+  /**
+   * Adds a style tag into the current context.
+   *
+   * @remarks
+   *
+   * You can pass a URL, filepath or string of contents. Note that when running Puppeteer
+   * in a browser environment you cannot pass a filepath and should use either
+   * `url` or `content`.
+   *
+   * @param options
+   */
   async addStyleTag(options: {
     url?: string;
     path?: string;
@@ -320,6 +344,14 @@ export class DOMWorld {
     }
 
     if (path !== null) {
+      if (!isNode) {
+        throw new Error(
+          'Cannot pass a filepath to addStyleTag in the browser environment.'
+        );
+      }
+      // eslint-disable-next-line @typescript-eslint/no-var-requires
+      const fs = require('fs');
+      const readFileAsync = helper.promisify(fs.readFile);
       let contents = await readFileAsync(path, 'utf8');
       contents += '/*# sourceURL=' + path.replace(/\n/g, '') + '*/';
       const context = await this.executionContext();

src/common/Debug.ts

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-const isNodeEnv = typeof document === 'undefined';
+import { isNode } from '../environment';
 
 /**
  * A debug function that can be used in any environment.
@@ -35,7 +35,7 @@ const isNodeEnv = typeof document === 'undefined';
  * ```
  */
 export const debug = (prefix: string): ((...args: unknown[]) => void) => {
-  if (isNodeEnv) {
+  if (isNode) {
     // eslint-disable-next-line @typescript-eslint/no-var-requires
     return require('debug')(prefix);
   }

src/environment.ts

@@ -0,0 +1,17 @@
+/**
+ * Copyright 2020 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export const isNode = typeof document === 'undefined';