问题描述

我是 node.js 的新手，我正在尝试要求一个类.我用过 https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Classes 作为参考.但是，例如，当我这样做时:

I am new to node.js and I am trying to require a class. I have used https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Classes as reference. However, when I do this for example:

// talker.js
class Talker {
    talk(msg) {
        console.log(this.say(msg))
        var t = setTimeout(this.talk, 5000, 'hello again');
    }
    say(msg) {
        return msg
    }
}
export default Talker

// app.js
import Talker from './taker.js'
const talker = new Talker()
talker.talk('hello')

我明白了:

talker.js:4 Uncaught TypeError: this.say 不是函数

talker.js:4 Uncaught TypeError: this.say is not a function

应该说app.js是electron.js的渲染进程，使用rollup.js捆绑

It should be said that app.js is the electron.js renderer process and it bundled using rollup.js

任何想法为什么会这样?

Any ideas why this would be?

更新:抱歉，我在输入伪代码时忘记添加一行.当我用回调调用 setTimeout 时，它实际上会发生.我已经更新了代码.

Update: Sorry, I forgot to add in a line when putting in the psuedo code. It actually happens when I call setTimeout with callback. I have updated the code.

推荐答案

你正在失去 this 对你的方法的绑定.

You are losing the bind of this to your method.

从此改变:

setTimeout(this.talk, 5000, 'hello again');

到这里:

setTimeout(this.talk.bind(this), 5000, 'hello again');

<小时>

当您将 this.talk 作为函数参数传递时，它接受 this 并查找方法 talk 并传递对该方法的引用功能.但是，它只传递对该函数的引用.与您在 this 中的对象不再有任何关联..bind() 允许您将引用传递给一个小存根函数，该函数将跟踪 this 并将您的方法称为 this.say()，而不仅仅是 say().

When you pass this.talk as a function argument, it takes this and looks up the method talk and passes a reference to that function. But, it only passes a reference to that function. There is no longer any association with the object you had in this. .bind() allows you to pass a reference to a tiny stub function that will keep track of this and call your method as this.say(), not just as say().

如果你这样做，你会看到同样的事情:

You can see the same thing if you just did this:

const talker = new Talker();'

const fn = talker.say;
fn();

这会产生同样的问题，因为将方法分配给 fn 根本不会与 talker 关联.它只是一个函数引用，与对象没有任何关联.事实上:

This would generate the same issue because assigning the method to fn takes no associate to talker with it at all. It's just a function reference without any association with an object. In fact:

talker.say === Talker.prototype.say

.bind() 所做的是创建一个小的存根函数，该函数将保存对象值，然后使用该对象调用您的方法.

What .bind() does is create a small stub function that will save the object value and will then call your method using that object.

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