class Downloader { constructor(data, options) { this.data = data; this.options = options; this.item = null; this.onStart = null; this.onProgress = null; this.onCompleted = null; this.data.progress = 0; // 新增 progress 属性 this.data.status='pause';//true 表示 进度没有结束，继续下载 this.data.timeid=0; } start() { const win = BrowserWindow.getFocusedWindow(); this.options.onStarted = (item) => { this.item = item; this.data.status='process';//true 表示 进度没有结束，继续下载 this.onStart(); }; this.options.onTotalProgress=(progress)=>{ this.data.progress = progress.percent * 100; // 更新 progress 属性 this.onTotalProgress(progress); } this.options.onCompleted = () => { this.onCompleted(); }; download(win, this.data.dowloadLink, this.options); } pause() { if (this.item) { this.item.pause(); } } resume() { if (this.item) { this.item.resume(); } } cancel() { if (this.item) { this.item.cancel(); } } } 这个下载器，里面的方法没有挂载到对象上是什么原因。、

这个下载器中的方法没有挂载到对象上是因为它们是定义在 Downloader 类的原型上的。在 JavaScript 中，类的方法通常都是定义在原型上的，而不是在对象实例上。这样做的好处是可以节省内存，因为所有的对象实例都可以共享同一个方法实现。当我们创建一个类的实例时，JavaScript 引擎会自动将该实例的原型指向该类的原型，因此该实例就可以访问该类的所有方法。

相关问题

// 下载器类 class Downloader { constructor(data, options) { this.data = data; this.options = options; this.item = null; this.onStart = null; this.onProgress = null; this.onCompleted = null; this.data.progress = 0; // 新增 progress 属性 this.data.status='pause';//true 表示 进度没有结束，继续下载 this.data.timeid=0; } start() { const win = BrowserWindow.getFocusedWindow(); this.options.onStarted = (item) => { this.item = item; this.data.status='process';//true 表示 进度没有结束，继续下载 this.onStart(); }; this.options.onTotalProgress=(progress)=>{ this.data.progress = progress.percent * 100; // 更新 progress 属性 this.onTotalProgress(progress); } this.options.onCompleted = () => { this.onCompleted(); }; download(win, this.data.dowloadLink, this.options); } pause() { if (this.item) { this.item.pause(); } } resume() { if (this.item) { this.item.resume(); } } cancel() { if (this.item) { this.item.cancel(); } } } 这是我说的类，里面有异步方法，怎么实现

你可以在异步方法执行完毕后，通过 Promise 或回调函数的方式通知外部代码。例如，在 onCompleted 回调函数中设置一个 Promise，然后在外部代码中等待这个 Promise 执行完毕，再执行下一步操作。类似下面这样：

class Downloader {
  constructor(data, options) {
    this.data = data;
    this.options = options;
    this.item = null;
    this.onStart = null;
    this.onProgress = null;
    this.onCompleted = null;
    this.data.progress = 0;
    this.data.status = 'pause';
    this.data.timeid = 0;
  }

  start() {
    const win = BrowserWindow.getFocusedWindow();
    this.options.onStarted = (item) => {
      this.item = item;
      this.data.status = 'process';
      this.onStart();
    };

    this.options.onTotalProgress = (progress) => {
      this.data.progress = progress.percent * 100;
      this.onTotalProgress(progress);
    };

    this.options.onCompleted = () => {
      this.onCompletedPromise.resolve(); // 执行 Promise
    };

    this.onCompletedPromise = {}; // 保存 Promise 对象
    this.onCompletedPromise.promise = new Promise((resolve, reject) => {
      this.onCompletedPromise.resolve = resolve;
      this.onCompletedPromise.reject = reject;
    });

    download(win, this.data.dowloadLink, this.options);
  }

  async pause() {
    if (this.item) {
      await this.onCompletedPromise; // 等待 Promise 执行完毕
      this.item.pause();
    }
  }

  async resume() {
    if (this.item) {
      await this.onCompletedPromise; // 等待 Promise 执行完毕
      this.item.resume();
    }
  }

  async cancel() {
    if (this.item) {
      await this.onCompletedPromise; // 等待 Promise 执行完毕
      this.item.cancel();
    }
  }
}

这样就能保证异步方法执行完毕后再执行外部代码了。

electron-dl 创建了一个类，用户管理多个下载器，但是我无法拿到每个下载器的进度条。 // 下载器类 class Downloader { constructor(data, options) { this.data = data; this.options = options; this.item = null; this.onStart = null; this.onProgress = null; this.onCompleted = null; } start() { const win = BrowserWindow.getFocusedWindow(); this.options.onStarted = (item) => { this.item = item; if (this.onStart) { this.onStart(); } }; this.options.onProgress = (progress) => { if (this.onProgress) { this.onProgress(progress); } }; this.options.onCompleted = () => { if (this.onCompleted) { this.onCompleted(); } }; download(win, this.data.dowloadLink, this.options); } pause() { if (this.item) { this.item.pause(); } } resume() { if (this.item) { this.item.resume(); } } cancel() { if (this.item) { this.item.cancel(); } } }

如果你想要获取每个下载器的进度条，你可以在 Downloader 类中添加一个 progress 属性，用于存储每个下载器的进度。然后在 onProgress 回调函数中更新该属性的值。这样，你就可以通过调用 Downloader 实例的 progress 属性来获取每个下载器的进度条了。以下是修改后的代码示例：

class Downloader {
  constructor(data, options) {
    this.data = data;
    this.options = options;
    this.item = null;
    this.onStart = null;
    this.onProgress = null;
    this.onCompleted = null;
    this.progress = 0; // 新增 progress 属性
  }

  start() {
    const win = BrowserWindow.getFocusedWindow();

    this.options.onStarted = (item) => {
      this.item = item;

      if (this.onStart) {
        this.onStart();
      }
    };

    this.options.onProgress = (progress) => {
      this.progress = progress; // 更新 progress 属性

      if (this.onProgress) {
        this.onProgress(progress);
      }
    };

    this.options.onCompleted = () => {
      if (this.onCompleted) {
        this.onCompleted();
      }
    };

    download(win, this.data.dowloadLink, this.options);
  }

  pause() {
    if (this.item) {
      this.item.pause();
    }
  }

  resume() {
    if (this.item) {
      this.item.resume();
    }
  }

  cancel() {
    if (this.item) {
      this.item.cancel();
    }
  }
}