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
    }
}

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>
    `
}

权宜之计

你可以创建一个async init(){…返回this;}方法，然后执行new MyClass().init()，当你通常只说new MyClass()时。

这并不干净，因为它依赖于使用您的代码的每个人，以及您自己，总是像这样实例化对象。但是，如果您只在代码中的一两个特定位置使用该对象，则可能没有问题。

但是一个重要的问题出现了，因为ES没有类型系统，所以如果你忘记调用它，你只是返回了undefined，因为构造函数没有返回任何东西。哦。更好的做法是这样做:

最好的办法是:

class AsyncOnlyObject {
    constructor() {
    }
    async init() {
        this.someField = await this.calculateStuff();
    }

    async calculateStuff() {
        return 5;
    }
}

async function newAsync_AsyncOnlyObject() {
    return await new AsyncOnlyObject().init();
}

newAsync_AsyncOnlyObject().then(console.log);
// output: AsyncOnlyObject {someField: 5}

工厂方法解决方案(稍好)

然而，你可能会意外地做新的AsyncOnlyObject，你应该直接创建使用Object.create(AsyncOnlyObject.prototype)的工厂函数:

async function newAsync_AsyncOnlyObject() {
    return await Object.create(AsyncOnlyObject.prototype).init();
}

newAsync_AsyncOnlyObject().then(console.log);
// output: AsyncOnlyObject {someField: 5}

However say you want to use this pattern on many objects... you could abstract this as a decorator or something you (verbosely, ugh) call after defining like postProcess_makeAsyncInit(AsyncOnlyObject), but here I'm going to use extends because it sort of fits into subclass semantics (subclasses are parent class + extra, in that they should obey the design contract of the parent class, and may do additional things; an async subclass would be strange if the parent wasn't also async, because it could not be initialized the same way):

抽象解决方案(扩展/子类版本)

class AsyncObject {
    constructor() {
        throw new Error('classes descended from AsyncObject must be initialized as (await) TheClassName.anew(), rather than new TheClassName()');
    }

    static async anew(...args) {
        var R = Object.create(this.prototype);
        R.init(...args);
        return R;
    }
}

class MyObject extends AsyncObject {
    async init(x, y=5) {
        this.x = x;
        this.y = y;
        // bonus: we need not return 'this'
    }
}

MyObject.anew('x').then(console.log);
// output: MyObject {x: "x", y: 5}

(不要在生产中使用:我没有考虑过复杂的场景，比如这是否是为关键字参数编写包装器的正确方式。)

这里有很多伟大的知识和一些超级()深思熟虑的回答。简而言之，下面概述的技术相当简单、非递归、异步兼容，并且遵循规则。更重要的是，我认为这里还没有正确地覆盖它-尽管如果错误请纠正我!

我们不调用方法，而是简单地将II(A)FE赋值给实例prop:

// it's async-lite!
class AsyncLiteComponent {
  constructor() {
    // our instance includes a 'ready' property: an IIAFE promise
    // that auto-runs our async needs and then resolves to the instance
    // ...
    // this is the primary difference to other answers, in that we defer
    // from a property, not a method, and the async functionality both
    // auto-runs and the promise/prop resolves to the instance
    this.ready = (async () => {
      // in this example we're auto-fetching something
      this.msg = await AsyncLiteComponent.msg;
      // we return our instance to allow nifty one-liners (see below)
      return this;
    })();
  }

  // we keep our async functionality in a static async getter
  // ... technically (with some minor tweaks), we could prefetch
  // or cache this response (but that isn't really our goal here)
  static get msg() {
    // yes I know - this example returns almost immediately (imagination people!)
    return fetch('data:,Hello%20World%21').then((e) => e.text());
  }
}

看起来很简单，怎么用呢?

// Ok, so you *could* instantiate it the normal, excessively boring way
const iwillnotwait = new AsyncLiteComponent();
// and defer your waiting for later
await iwillnotwait.ready
console.log(iwillnotwait.msg)

// OR OR OR you can get all async/awaity about it!
const onlywhenimready = await new AsyncLiteComponent().ready;
console.log(onlywhenimready.msg)

// ... if you're really antsy you could even "pre-wait" using the static method,
// but you'd probably want some caching / update logic in the class first
const prefetched = await AsyncLiteComponent.msg;

// ... and I haven't fully tested this but it should also be open for extension
class Extensior extends AsyncLiteComponent {
  constructor() {
    super();
    this.ready.then(() => console.log(this.msg))
  } 
}
const extendedwaittime = await new Extensior().ready;

在发帖之前，我在@slebetman的评论中对这种技术的可行性进行了简短的讨论。我并没有完全被这种直接的解雇所说服，所以我认为我应该进一步讨论/推翻它。请尽你最大的努力吧。

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)
}

不像其他人说的，你可以让它工作。

JavaScript类可以从它们的构造函数返回任何东西，甚至是另一个类的实例。因此，您可以从解析到其实际实例的类的构造函数返回一个Promise。

下面是一个例子:

export class Foo {

    constructor() {

        return (async () => {

            // await anything you want

            return this; // Return the newly-created instance
        })();
    }
}

然后，你将这样创建Foo的实例:

const foo = await new Foo();