再次 setTimeout 与 setInterval

发布于 2024-12-12 00:13:02 字数 490 浏览 2 评论 0原文

所以我知道 setTimeout 和 setInterval 之间存在差异，但请考虑这两个代码示例：

function myFunction(){
   setTimeout('myFunction();', 100);
   doSomething();
}
setTimeout('myFunction();', 100);

并且

function myFunction(){
   doSomething();
}
setInterval('myFunction();', 100);

请注意，在第一个示例中我调用 setTimeout在函数的开头，然后我doSomething。因此，doSomething() 不会产生额外的延迟。这是否意味着这两个示例的作用完全相同？还是还有更细微的差别？

原文

So I know that there are differences between setTimeout and setInterval, but consider these two code examples:

function myFunction(){
   setTimeout('myFunction();', 100);
   doSomething();
}
setTimeout('myFunction();', 100);

and

function myFunction(){
   doSomething();
}
setInterval('myFunction();', 100);

Note that in the first example I call setTimeout at the begining of the function and then I doSomething. Therefore there is no extra delay from doSomething(). Does that mean that those two examples do exactly the same? Or is there even more subtle difference?

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只怪假的太真实 2024-12-19 00:13:02

它们在功能上大致相同，但也存在差异。一个区别在于，如果 doSomething 花费的时间比间隔长，浏览器如何处理它。使用setInterval，如果doSomething仍在运行，至少某些浏览器将跳过下一个间隔。因此，如果您使用 100 毫秒，并且 doSomething 需要 110 毫秒来运行，则下一次运行要等到 90 毫秒后才会发生（当然，所有这些时间都是近似值）。

另一个区别是，使用 setTimeout 时，您每次都会获得一个新句柄，而使用 setInterval 时，您只会获得一个句柄。

与给出的示例的另一个区别是，在 setTimeout 示例中，您每次都会启动 JavaScript 解析器/编译器，而使用 setInterval 你只启动解析器/编译器一次。但这种差异并不重要，因为您根本不应该这样做 - 见下文。

但抛开细微差别不谈，你所拥有的功能在功能上是相同的。

旁注：将字符串传递到 setTimeout 或 setInterval 中都不是最佳实践。相反，传入一个函数引用：

// setTimeout
function myFunction(){
   setTimeout(myFunction, 100);
   doSomething();
}
setTimeout(myFunction, 100);

// setInterval
function myFunction(){
   doSomething();
}
setInterval(myFunction, 100);

传入一个字符串会启动 JavaScript 解析器并执行与 eval 相同的操作。应尽可能避免（而且几乎总是可能的）。

They're functionally about the same, but there are differences. One difference is in how browsers handle it if doSomething takes longer than the interval. With setInterval, at least some browsers will just skip the next interval if doSomething is still running. So if you use 100ms as you have, and doSomething takes 110 ms to run, the next run won't happen until 90ms later (of course, all of these times are approximate).

Another difference is that with the setTimeout, you'll get a new handle every time, whereas with setInterval you get one handle.

Another difference with your examples as given is that in the setTimeout example, you're firing up a JavaScript parser/compiler every time, whereas with setInterval you're only firing up the parser/compiler once. But this difference shouldn't matter, because you shouldn't be doing that at all — see below.

But subtleties aside, what you have there is functionally the same.

Side note: It's not best practice to pass strings into either setTimeout or setInterval. Instead, pass in a function reference:

// setTimeout
function myFunction(){
   setTimeout(myFunction, 100);
   doSomething();
}
setTimeout(myFunction, 100);

// setInterval
function myFunction(){
   doSomething();
}
setInterval(myFunction, 100);

Passing in a string fires up a JavaScript parser and does the same thing as eval. It should be avoided whenever possible (and it's almost always possible).

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