問題描述

我是 node.js 的新手，我正在嘗試要求一個類.我用過 https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Classes 作為參考.但是，例如，當我這樣做時:

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 不是函數

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

應該說app.js是electron.js的渲染進程，使用rollup.js捆綁

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

任何想法為什么會這樣?

Any ideas why this would be?

更新:抱歉，我在輸入偽代碼時忘記添加一行.當我用回調調用 setTimeout 時，它實際上會發生.我已經更新了代碼.

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.

推薦答案

你正在失去 this 對你的方法的綁定.

You are losing the bind of this to your method.

從此改變:

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

到這里:

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

<小時>

當您將 this.talk 作為函數參數傳遞時，它接受 this 并查找方法 talk 并傳遞對該方法的引用功能.但是，它只傳遞對該函數的引用.與您在 this 中的對象不再有任何關聯..bind() 允許您將引用傳遞給一個小存根函數，該函數將跟蹤 this 并將您的方法稱為 this.say()，而不僅僅是 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().

如果你這樣做，你會看到同樣的事情:

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

const talker = new Talker();'

const fn = talker.say;
fn();

這會產生同樣的問題，因為將方法分配給 fn 根本不會與 talker 關聯.它只是一個函數引用，與對象沒有任何關聯.事實上:

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() 所做的是創建一個小的存根函數，該函數將保存對象值，然后使用該對象調用您的方法.

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

這篇關于未捕獲的類型錯誤:this.method 不是函數 - 節點 js 類導出的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！