anchor.diff:  (function() {
     "use strict";
     class FlutterLoader {
  -    // TODO: Move the below methods to "#private" once supported by all the browsers
  -    // we support. In the meantime, we use the "revealing module" pattern.
  +    /**
  +     * Creates a FlutterLoader, and initializes its instance methods.
  +     */
  +    constructor() {
  +      // TODO: Move the below methods to "#private" once supported by all the browsers
  +      // we support. In the meantime, we use the "revealing module" pattern.
   
  -    // Watchdog to prevent injecting the main entrypoint multiple times.
  -    _scriptLoaded = null;
  +      // Watchdog to prevent injecting the main entrypoint multiple times.
  +      this._scriptLoaded = null;
   
  -    // Resolver for the pending promise returned by loadEntrypoint.
  -    _didCreateEngineInitializerResolve = null;
  +      // Resolver for the pending promise returned by loadEntrypoint.
  +      this._didCreateEngineInitializerResolve = null;
  +
  +      // Called by Flutter web.
  +      // Bound to `this` now, so "this" is preserved across JS <-> Flutter jumps.
  +      this.didCreateEngineInitializer = this._didCreateEngineInitializer.bind(this);
  +    }
   
       /**
        * Initializes the main.dart.js with/without serviceWorker.
  
positive.code:           let scriptTag = document.createElement("script");
            scriptTag.src = entrypointUrl;
            scriptTag.type = "application/javascript";
            this._didCreateEngineInitializerResolve = resolve; // Cache the resolve, so it can be called from Flutter.
            scriptTag.addEventListener("error", reject);
            document.body.append(scriptTag);
          });
  
negative.code:     }
  
      /**
       * Resolves the promise created by loadEntrypoint.
       * Called by Flutter through the public `didCreateEngineInitializer` method,
       * which is bound to the correct instance of the FlutterLoader on the page.
       * @param {*} engineInitializer
       */
      _didCreateEngineInitializer(engineInitializer) {
        if (typeof this._didCreateEngineInitializerResolve != "function") {
          console.warn("Do not call didCreateEngineInitializer by hand. Start with loadEntrypoint instead.");
        }
        this._didCreateEngineInitializerResolve(engineInitializer);
        // Remove the public method after it's done, so Flutter Web can hot restart.
        delete this.didCreateEngineInitializer;
      }
  
      _loadEntrypoint(entrypointUrl) {
        if (!this._scriptLoaded) {
  