flutter.js

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

if (!_flutter) {
  var _flutter = {};
}
_flutter.loader = null;

(function () {
  "use strict";

  const baseUri = ensureTrailingSlash(getBaseURI());

  function getBaseURI() {
    const base = document.querySelector("base");
    return (base && base.getAttribute("href")) || "";
  }

  function ensureTrailingSlash(uri) {
    if (uri == "") {
      return uri;
    }
    return uri.endsWith("/") ? uri : `${uri}/`;
  }

  /**
   * Wraps `promise` in a timeout of the given `duration` in ms.
   *
   * Resolves/rejects with whatever the original `promises` does, or rejects
   * if `promise` takes longer to complete than `duration`. In that case,
   * `debugName` is used to compose a legible error message.
   *
   * If `duration` is < 0, the original `promise` is returned unchanged.
   * @param {Promise} promise
   * @param {number} duration
   * @param {string} debugName
   * @returns {Promise} a wrapped promise.
   */
  async function timeout(promise, duration, debugName) {
    if (duration < 0) {
      return promise;
    }
    let timeoutId;
    const _clock = new Promise((_, reject) => {
      timeoutId = setTimeout(() => {
        reject(
          new Error(
            `${debugName} took more than ${duration}ms to resolve. Moving on.`,
            {
              cause: timeout,
            }
          )
        );
      }, duration);
    });

    return Promise.race([promise, _clock]).finally(() => {
      clearTimeout(timeoutId);
    });
  }

  /**
   * Handles the creation of a TrustedTypes `policy` that validates URLs based
   * on an (optional) incoming array of RegExes.
   */
  class FlutterTrustedTypesPolicy {
    /**
     * Constructs the policy.
     * @param {[RegExp]} validPatterns the patterns to test URLs
     * @param {String} policyName the policy name (optional)
     */
    constructor(validPatterns, policyName = "flutter-js") {
      const patterns = validPatterns || [
        /\.js$/,
      ];
      if (window.trustedTypes) {
        this.policy = trustedTypes.createPolicy(policyName, {
          createScriptURL: function(url) {
            const parsed = new URL(url, window.location);
            const file = parsed.pathname.split("/").pop();
            const matches = patterns.some((pattern) => pattern.test(file));
            if (matches) {
              return parsed.toString();
            }
            console.error(
              "URL rejected by TrustedTypes policy",
              policyName, ":", url, "(download prevented)");
          }
        });
      }
    }
  }

  /**
   * Handles loading/reloading Flutter's service worker, if configured.
   *
   * @see: https://developers.google.com/web/fundamentals/primers/service-workers
   */
  class FlutterServiceWorkerLoader {
    /**
     * Injects a TrustedTypesPolicy (or undefined if the feature is not supported).
     * @param {TrustedTypesPolicy | undefined} policy
     */
    setTrustedTypesPolicy(policy) {
      this._ttPolicy = policy;
    }

    /**
     * Returns a Promise that resolves when the latest Flutter service worker,
     * configured by `settings` has been loaded and activated.
     *
     * Otherwise, the promise is rejected with an error message.
     * @param {*} settings Service worker settings
     * @returns {Promise} that resolves when the latest serviceWorker is ready.
     */
    loadServiceWorker(settings) {
      if (settings == null) {
        // In the future, settings = null -> uninstall service worker?
        console.debug("Null serviceWorker configuration. Skipping.");
        return Promise.resolve();
      }
      if (!("serviceWorker" in navigator)) {
        let errorMessage = "Service Worker API unavailable.";
        if (!window.isSecureContext) {
          errorMessage += "\nThe current context is NOT secure."
          errorMessage += "\nRead more: https://developer.mozilla.org/en-US/docs/Web/Security/Secure_Contexts";
        }
        return Promise.reject(
          new Error(errorMessage)
        );
      }
      const {
        serviceWorkerVersion,
        serviceWorkerUrl = `${baseUri}flutter_service_worker.js?v=${serviceWorkerVersion}`,
        timeoutMillis = 4000,
      } = settings;

      // Apply the TrustedTypes policy, if present.
      let url = serviceWorkerUrl;
      if (this._ttPolicy != null) {
        url = this._ttPolicy.createScriptURL(url);
      }

      const serviceWorkerActivation = navigator.serviceWorker
        .register(url)
        .then(this._getNewServiceWorker)
        .then(this._waitForServiceWorkerActivation);

      // Timeout race promise
      return timeout(
        serviceWorkerActivation,
        timeoutMillis,
        "prepareServiceWorker"
      );
    }

    /**
     * Returns the latest service worker for the given `serviceWorkerRegistrationPromise`.
     *
     * This might return the current service worker, if there's no new service worker
     * awaiting to be installed/updated.
     *
     * @param {Promise<ServiceWorkerRegistration>} serviceWorkerRegistrationPromise
     * @returns {Promise<ServiceWorker>}
     */
    async _getNewServiceWorker(serviceWorkerRegistrationPromise) {
      const reg = await serviceWorkerRegistrationPromise;

      if (!reg.active && (reg.installing || reg.waiting)) {
        // No active web worker and we have installed or are installing
        // one for the first time. Simply wait for it to activate.
        console.debug("Installing/Activating first service worker.");
        return reg.installing || reg.waiting;
      } else if (!reg.active.scriptURL.endsWith(serviceWorkerVersion)) {
        // When the app updates the serviceWorkerVersion changes, so we
        // need to ask the service worker to update.
        return reg.update().then((newReg) => {
          console.debug("Updating service worker.");
          return newReg.installing || newReg.waiting || newReg.active;
        });
      } else {
        console.debug("Loading from existing service worker.");
        return reg.active;
      }
    }

    /**
     * Returns a Promise that resolves when the `latestServiceWorker` changes its
     * state to "activated".
     *
     * @param {Promise<ServiceWorker>} latestServiceWorkerPromise
     * @returns {Promise<void>}
     */
    async _waitForServiceWorkerActivation(latestServiceWorkerPromise) {
      const serviceWorker = await latestServiceWorkerPromise;

      if (!serviceWorker || serviceWorker.state == "activated") {
        if (!serviceWorker) {
          return Promise.reject(
            new Error("Cannot activate a null service worker!")
          );
        } else {
          console.debug("Service worker already active.");
          return Promise.resolve();
        }
      }
      return new Promise((resolve, _) => {
        serviceWorker.addEventListener("statechange", () => {
          if (serviceWorker.state == "activated") {
            console.debug("Activated new service worker.");
            resolve();
          }
        });
      });
    }
  }

  /**
   * Handles injecting the main Flutter web entrypoint (main.dart.js), and notifying
   * the user when Flutter is ready, through `didCreateEngineInitializer`.
   *
   * @see https://docs.flutter.dev/development/platform-integration/web/initialization
   */
  class FlutterEntrypointLoader {
    /**
     * Creates a FlutterEntrypointLoader.
     */
    constructor() {
      // Watchdog to prevent injecting the main entrypoint multiple times.
      this._scriptLoaded = false;
    }

    /**
     * Injects a TrustedTypesPolicy (or undefined if the feature is not supported).
     * @param {TrustedTypesPolicy | undefined} policy
     */
    setTrustedTypesPolicy(policy) {
      this._ttPolicy = policy;
    }

    /**
     * Loads flutter main entrypoint, specified by `entrypointUrl`, and calls a
     * user-specified `onEntrypointLoaded` callback with an EngineInitializer
     * object when it's done.
     *
     * @param {*} options
     * @returns {Promise | undefined} that will eventually resolve with an
     * EngineInitializer, or will be rejected with the error caused by the loader.
     * Returns undefined when an `onEntrypointLoaded` callback is supplied in `options`.
     */
    async loadEntrypoint(options) {
      const { entrypointUrl = `${baseUri}main.dart.js`, onEntrypointLoaded } =
        options || {};

      return this._loadEntrypoint(entrypointUrl, onEntrypointLoaded);
    }

    /**
     * Resolves the promise created by loadEntrypoint, and calls the `onEntrypointLoaded`
     * function supplied by the user (if needed).
     *
     * Called by Flutter through `_flutter.loader.didCreateEngineInitializer` method,
     * which is bound to the correct instance of the FlutterEntrypointLoader by
     * the FlutterLoader object.
     *
     * @param {Function} engineInitializer @see https://github.com/flutter/engine/blob/main/lib/web_ui/lib/src/engine/js_interop/js_loader.dart#L42
     */
    didCreateEngineInitializer(engineInitializer) {
      if (typeof this._didCreateEngineInitializerResolve === "function") {
        this._didCreateEngineInitializerResolve(engineInitializer);
        // Remove the resolver after the first time, so Flutter Web can hot restart.
        this._didCreateEngineInitializerResolve = null;
        // Make the engine revert to "auto" initialization on hot restart.
        delete _flutter.loader.didCreateEngineInitializer;
      }
      if (typeof this._onEntrypointLoaded === "function") {
        this._onEntrypointLoaded(engineInitializer);
      }
    }

    /**
     * Injects a script tag into the DOM, and configures this loader to be able to
     * handle the "entrypoint loaded" notifications received from Flutter web.
     *
     * @param {string} entrypointUrl the URL of the script that will initialize
     *                 Flutter.
     * @param {Function} onEntrypointLoaded a callback that will be called when
     *                   Flutter web notifies this object that the entrypoint is
     *                   loaded.
     * @returns {Promise | undefined} a Promise that resolves when the entrypoint
     *                                is loaded, or undefined if `onEntrypointLoaded`
     *                                is a function.
     */
    _loadEntrypoint(entrypointUrl, onEntrypointLoaded) {
      const useCallback = typeof onEntrypointLoaded === "function";

      if (!this._scriptLoaded) {
        this._scriptLoaded = true;
        const scriptTag = this._createScriptTag(entrypointUrl);
        if (useCallback) {
          // Just inject the script tag, and return nothing; Flutter will call
          // `didCreateEngineInitializer` when it's done.
          console.debug("Injecting <script> tag. Using callback.");
          this._onEntrypointLoaded = onEntrypointLoaded;
          document.body.append(scriptTag);
        } else {
          // Inject the script tag and return a promise that will get resolved
          // with the EngineInitializer object from Flutter when it calls
          // `didCreateEngineInitializer` later.
          return new Promise((resolve, reject) => {
            console.debug(
              "Injecting <script> tag. Using Promises. Use the callback approach instead!"
            );
            this._didCreateEngineInitializerResolve = resolve;
            scriptTag.addEventListener("error", reject);
            document.body.append(scriptTag);
          });
        }
      }
    }

    /**
     * Creates a script tag for the given URL.
     * @param {string} url
     * @returns {HTMLScriptElement}
     */
    _createScriptTag(url) {
      const scriptTag = document.createElement("script");
      scriptTag.type = "application/javascript";
      // Apply TrustedTypes validation, if available.
      let trustedUrl = url;
      if (this._ttPolicy != null) {
        trustedUrl = this._ttPolicy.createScriptURL(url);
      }
      scriptTag.src = trustedUrl;
      return scriptTag;
    }
  }

  /**
   * The public interface of _flutter.loader. Exposes two methods:
   * * loadEntrypoint (which coordinates the default Flutter web loading procedure)
   * * didCreateEngineInitializer (which is called by Flutter to notify that its
   *                              Engine is ready to be initialized)
   */
  class FlutterLoader {
    /**
     * Initializes the Flutter web app.
     * @param {*} options
     * @returns {Promise?} a (Deprecated) Promise that will eventually resolve
     *                     with an EngineInitializer, or will be rejected with
     *                     any error caused by the loader. Or Null, if the user
     *                     supplies an `onEntrypointLoaded` Function as an option.
     */
    async loadEntrypoint(options) {
      const { serviceWorker, ...entrypoint } = options || {};

      // A Trusted Types policy that is going to be used by the loader.
      const flutterTT = new FlutterTrustedTypesPolicy();

      // The FlutterServiceWorkerLoader instance could be injected as a dependency
      // (and dynamically imported from a module if not present).
      const serviceWorkerLoader = new FlutterServiceWorkerLoader();
      serviceWorkerLoader.setTrustedTypesPolicy(flutterTT.policy);
      await serviceWorkerLoader.loadServiceWorker(serviceWorker).catch(e => {
        // Regardless of what happens with the injection of the SW, the show must go on
        console.warn("Exception while loading service worker:", e);
      });

      // The FlutterEntrypointLoader instance could be injected as a dependency
      // (and dynamically imported from a module if not present).
      const entrypointLoader = new FlutterEntrypointLoader();
      entrypointLoader.setTrustedTypesPolicy(flutterTT.policy);
      // Install the `didCreateEngineInitializer` listener where Flutter web expects it to be.
      this.didCreateEngineInitializer =
        entrypointLoader.didCreateEngineInitializer.bind(entrypointLoader);
      return entrypointLoader.loadEntrypoint(entrypoint);
    }
  }

  _flutter.loader = new FlutterLoader();
})();