为什么 setTimeout 需要匿名函数才能工作? [英] Why does setTimeout require anonymous function to work?

问题描述

我正在阅读 StackOverflow 上的一个答案这里，其中解释了如何使用 setTimeout 在网页.但是，我想知道为什么 setTimeout 需要匿名函数才能工作.考虑以下代码:

I was reading an answer on StackOverflow here that explained how to use setTimeout to create a sort of recurring loop on a webpage. However, I am wondering why setTimeout requires an anonymous function to work. Consider the following code:

trainingTimer(60,0);

function trainingTimer(duration,c) {
    document.getElementById("timer").innerHTML = "Time left: "+(duration-c);
    if(duration==c) {
        alert("Time is up!");
    }
    else {
        window.setTimeout(trainingTimer(duration,c+1),1000);
    }
}

我根据上面链接的答案写了这个，但是当它运行时，它会一次循环所有 60 个 trainingTimer 调用，并立即在我的网页上显示剩余时间:0".但是，如果我修改

I wrote this based off the answer that I linked above, however when it runs it loops through all 60 trainingTimer calls at once, and immediately displays "Time left: 0" on my web page. However, if I modify

window.setTimeout(trainingTimer(duration,c+1),1000);

并将 trainingTimer(duration,c+1) 包裹在一个匿名函数中

and wrap trainingTimer(duration,c+1) in an anonymous function like so

window.setTimeout(function() {trainingTimer(duration,c+1)},1000);

然后代码运行得很好.

我想知道为什么我必须将命名函数包装在匿名函数中才能使 setInterval 正常工作.感谢大家的帮助.

I am wondering why I have to wrap a named function inside an anonymous function in order for setInterval to work properly. Thanks for all the help.

推荐答案

这个

window.setTimeout(trainingTimer(duration,c+1),1000); 

与

var result = trainingTimer(duration,c+1);
window.setTimeout(result,1000); 

它获取执行方法的结果并赋值.

It takes the result of the executed method and assigns it.

而且由于训练计时器方法没有返回任何内容.你的代码基本上是这样的

And since training timer method returns nothing. Your code is basically this

trainingTimer(duration,c+1);
window.setTimeout(undefined, 1000); 

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