目前,我正在尝试在类构造函数中使用async/await。这样我就可以为我正在进行的Electron项目获得一个自定义的电子邮件标签。

customElements.define('e-mail', class extends HTMLElement {
  async constructor() {
    super()

    let uid = this.getAttribute('data-uid')
    let message = await grabUID(uid)

    const shadowRoot = this.attachShadow({mode: 'open'})
    shadowRoot.innerHTML = `
      <div id="email">A random email message has appeared. ${message}</div>
    `
  }
})

然而,目前项目不工作,有以下错误:

Class constructor may not be an async method

是否有一种方法来规避这一点,以便我可以使用异步/等待在这?而不是要求回调或.then()?


当前回答

您应该将该函数添加到实例中。Promise将它识别为Promise的可支持对象。解决自动

const asyncSymbol = Symbol();
class MyClass {
    constructor() {
        this.asyncData = null
    }
    then(resolve, reject) {
        return (this[asyncSymbol] = this[asyncSymbol] || new Promise((innerResolve, innerReject) => {
            this.asyncData = { a: 1 }
            setTimeout(() => innerResolve(this.asyncData), 3000)
        })).then(resolve, reject)
    }
}

async function wait() {
    const asyncData = await new MyClass();
    alert('run 3s later')
    alert(asyncData.a)
}

其他回答

你可以使用Proxy的构造句柄来做到这一点,代码如下:

const SomeClass = new Proxy(class A {
  constructor(user) {
    this.user = user;
  }
}, {
  async construct(target, args, newTarget) {
    const [name] = args;
    // you can use await in here
    const user = await fetch(name);
    // invoke new A here
    return new target(user);
  }
});

const a = await new SomeClass('cage');
console.log(a.user); // user info

最接近异步构造函数的方法是等待它完成执行,如果它还没有在它的所有方法中执行:

class SomeClass {
    constructor() {
        this.asyncConstructor = (async () => {
            // Perform asynchronous operations here
        })()
    }

    async someMethod() {
        await this.asyncConstructor
        // Perform normal logic here
    }
}

我通常更喜欢返回一个新实例的静态异步方法,但这里有另一种方法。它更接近于字面上的等待构造函数。它与TypeScript一起工作。

class Foo {
  #promiseReady;

  constructor() {
    this.#promiseReady = this.#init();
  }

  async #init() {
    await someAsyncStuff();
    return this;

  }

  ready() {
    return this.promiseReady;
  }
}
let foo = await new Foo().ready();

其他答案都忽略了一个显而易见的事实。简单地从你的构造函数调用一个async函数:

constructor() {
    setContentAsync();
}

async setContentAsync() {
    let uid = this.getAttribute('data-uid')
    let message = await grabUID(uid)

    const shadowRoot = this.attachShadow({mode: 'open'})
    shadowRoot.innerHTML = `
      <div id="email">A random email message has appeared. ${message}</div>
    `
}

您可以立即调用一个返回消息的匿名异步函数,并将其设置为message变量。如果您不熟悉这种模式,您可能想看看立即调用的函数表达式(IEFES)。这将非常有效。

var message = (async function() { return await grabUID(uid) })()