chrome/browser/resources/downloads/icon_loader.ts

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import {getFileIconUrl} from 'chrome://resources/js/icon.js';
import {PromiseResolver} from 'chrome://resources/js/promise_resolver.m.js';

export class IconLoader {
  private iconResolvers_: Map<string, PromiseResolver<boolean>>;
  private listeningImages_: Set<HTMLImageElement>;

  constructor() {
    this.iconResolvers_ = new Map();

    this.listeningImages_ = new Set();
  }

  /**
   * @return Whether or not the icon loaded successfully.
   */
  loadIcon(imageEl: HTMLImageElement, filePath: string): Promise<boolean> {
    const url = getFileIconUrl(filePath);

    if (!this.iconResolvers_.has(url)) {
      this.iconResolvers_.set(url, new PromiseResolver());
    }

    if (!this.listeningImages_.has(imageEl)) {
      imageEl.addEventListener('load', this.finishedLoading_.bind(this));
      imageEl.addEventListener('error', this.finishedLoading_.bind(this));
      this.listeningImages_.add(imageEl);
    }

    imageEl.src = url;

    return this.iconResolvers_.get(url)!.promise;
  }

  private finishedLoading_(e: Event) {
    const resolver =
        this.iconResolvers_.get((e.currentTarget as HTMLImageElement).src)!;
    if (!resolver.isFulfilled) {
      resolver.resolve(e.type === 'load');
    }
  }

  static getInstance(): IconLoader {
    return instance || (instance = new IconLoader());
  }

  static setInstance(obj: IconLoader) {
    instance = obj;
  }
}

let instance: IconLoader|null = null;