gecko-dev/toolkit/components/workerloader/require.js

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/**
 * Implementation of a CommonJS module loader for workers.
 *
 * Use:
 * // in the .js file loaded by the constructor of the worker
 * importScripts("resource://gre/modules/workers/require.js");
 * let module = require("resource://gre/modules/worker/myModule.js");
 *
 * // in myModule.js
 * // Load dependencies
 * let SimpleTest = require("resource://gre/modules/workers/SimpleTest.js");
 * let Logger = require("resource://gre/modules/workers/Logger.js");
 *
 * // Define things that will not be exported
 * let someValue = // ...
 *
 * // Export symbols
 * exports.foo = // ...
 * exports.bar = // ...
 *
 *
 * Note #1:
 * Properties |fileName| and |stack| of errors triggered from a module
 * contain file names that do not correspond to human-readable module paths.
 * Human readers should rather use properties |moduleName| and |moduleStack|.
 *
 * Note #2:
 * By opposition to some other module loader implementations, this module
 * loader does not enforce separation of global objects. Consequently, if
 * a module modifies a global object (e.g. |String.prototype|), all other
 * modules in the same worker may be affected.
 */

/* global require */
/* exported require */

(function (exports) {
  "use strict";

  if (exports.require) {
    // Avoid double-imports
    return;
  }

  // Simple implementation of |require|
  let require = (function () {
    /**
     * Mapping from module URI to module exports.
     *
     * @keys {string} The absolute URI to a module.
     * @values {object} The |exports| objects for that module.
     */
    let modules = new Map();

    /**
     * A human-readable version of |stack|.
     *
     * @type {string}
     */
    Object.defineProperty(Error.prototype, "moduleStack", {
      get() {
        return this.stack;
      },
    });
    /**
     * A human-readable version of |fileName|.
     *
     * @type {string}
     */
    Object.defineProperty(Error.prototype, "moduleName", {
      get() {
        let match = this.stack.match(/\@(.*):.*:/);
        if (match) {
          return match[1];
        }
        return "(unknown module)";
      },
    });

    /**
     * Import a module
     *
     * @param {string} baseURL The URL of the modules from which we load a new module.
     *        This will be null for the first loaded module and so expect an absolute URI in path.
     *        Note that this first parameter is bound before `require` method is passed outside
     *        of this module. So that typical callsites will only path the second `path` parameter.
     * @param {string} path The path to the module.
     * @return {*} An object containing the properties exported by the module.
     */
    return function require(baseURL, path) {
      let startTime = performance.now();
      if (typeof path != "string") {
        throw new TypeError(
          "The argument to require() must be a string got " + path
        );
      }

      // Resolve relative paths
      if ((path.startsWith("./") || path.startsWith("../")) && baseURL) {
        path = new URL(path, baseURL).href;
      }

      if (!path.includes("://")) {
        throw new TypeError(
          "The argument to require() must be a string uri, got " + path
        );
      }
      // Automatically add ".js" if there is no extension
      let uri;
      if (path.lastIndexOf(".") <= path.lastIndexOf("/")) {
        uri = path + ".js";
      } else {
        uri = path;
      }

      // Exports provided by the module
      let exports = Object.create(null);

      // Identification of the module
      let module = {
        id: path,
        uri,
        exports,
      };

      // Make module available immediately
      // (necessary in case of circular dependencies)
      if (modules.has(uri)) {
        return modules.get(uri).exports;
      }
      modules.set(uri, module);

      try {
        // Load source of module, synchronously
        let xhr = new XMLHttpRequest();
        xhr.open("GET", uri, false);
        xhr.responseType = "text";
        xhr.send();

        let source = xhr.responseText;
        if (source == "") {
          // There doesn't seem to be a better way to detect that the file couldn't be found
          throw new Error("Could not find module " + path);
        }
        // Use `Function` to leave this scope, use `eval` to start the line
        // number from 1 that is observed by `source` and the error message
        // thrown from the module, and also use `arguments` for accessing
        // `source` and `uri` to avoid polluting the module's environment.
        let code = new Function(
          "exports",
          "require",
          "module",
          `eval(arguments[3] + "\\n//# sourceURL=" + arguments[4] + "\\n")`
        );
        code(exports, require.bind(null, path), module, source, uri);
      } catch (ex) {
        // Module loading has failed, exports should not be made available
        // after all.
        modules.delete(uri);
        throw ex;
      } finally {
        ChromeUtils.addProfilerMarker("require", startTime, path);
      }

      Object.freeze(module.exports);
      Object.freeze(module);
      return module.exports;
    };
  })();

  Object.freeze(require);

  Object.defineProperty(exports, "require", {
    value: require.bind(null, null),
    enumerable: true,
    configurable: false,
  });
})(this);