为什么需要将匿名函数传递给onClick事件? [英] Why do I need to pass an anonymous function into the onClick event?

问题描述

我一直在尝试学习React的基础知识.但是，我遇到了本教程中的一节，要求我将 alert()放置在onClick事件中，例如:

I've been trying to learn the basics of React. However, I've come across a section in the tutorial that asks me to place an alert() inside of an onClick event as such:

        <button className="square" onClick={() => {alert("click");}}>
            {this.state.value}
        </button>

我不明白为什么需要箭头功能-为什么我不能仅仅拥有alert()?

I don't understand why the arrow function is required - why can't I just have the alert() on its own?

文档状态:

忘记()=>并编写onClick = {alert('click')}是一个常见错误，每次组件重新渲染时都会触发警报.

Forgetting () => and writing onClick={alert('click')} is a common mistake, and would fire the alert every time the component re-renders.

哪个是正确的-我已经尝试过了，它确实会不断调用 alert().但为什么?它不是应该在onClick而不是在render上触发吗?匿名函数做什么才能阻止这种行为?

Which is correct - I've tried this, and it does continually call alert(). But why? Isn't it supposed to fire onClick, and not on render? What does the anonymous function do that stops this behaviour?

推荐答案

因为如果调用一个函数，则该函数将运行.(然后您从中获得返回值)

Because if you call a function, then the function runs. (And you get the return value from it)

const onClick = alert("hello");
console.log(onClick);

如果您定义一个调用函数(Y)的函数(X)，那么直到您调用X时，它才调用Y.

If you define a function (X) that calls a function (Y), then it doesn't call Y until you call X.

const onClick = () => alert("hello");
console.log(onClick);

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