使用setTimeout（）的Javascript执行顺序 [英] Javascript execution order with setTimeout()

问题描述

假设我有以下代码：

function testA {
   setTimeout('testB()', 1000);
   doLong();
}

function testB {
   doSomething();
}

function doLong() {
   //takes a few seconds to do something
}

我执行 testA（）。我已经读过Javascript是单线程的。 1000毫秒后，当达到 testB（）的超时时会发生什么？

I execute testA(). I have read that Javascript is single-threaded. What happens after 1000 milliseconds, when the timeout for testB() is reached?

我能想到的一些可能性：

Some possibilities I can think of:

• testB（）在 doLong（）以及它调用的任何其他内容已完成。


• doLong（）立即终止并且 testB（）已启动。


• doLong（）获得一点点停止之前执行的时间更长（自动或在提示用户之后），并且 testB（）已启动。


• doLong（）暂停， testB（）已启动。在 testB（）完成后， doLong（）恢复。

• testB() is queued up to execute after doLong() and anything else it called have finished.
• doLong() is immediately terminated and testB() is started.
• doLong() is given a little while longer to execute before being stopped (either automatically or after prompting the user) and testB() is started.
• doLong() is paused, testB() is started. After testB() has finished, doLong() resumes.

答案是正确的？它是依赖于实现还是标准的一部分？*

What is the correct answer? Is it implementation dependant or part of the standard?*

这个问题类似但不一样，据我所知。

This question is similar but not the same, as far as I can tell.

为了更好地理解Javascript执行，你可以推荐任何链接我将不胜感激。

Any links that you can recommend for better understanding Javascript execution would be appreciated.

谢谢！

*是的，我知道并非所有浏览器都遵循标准：（

*Yes, I know that not all browsers follow standards :(

推荐答案

你猜测的第一个是正确的：
testB（）排队在doLong（）之后执行以及它调用的任何其他内容都已完成。

The first of your guesses is the correct one: testB() is queued up to execute after doLong() and anything else it called have finished.

如果需要超过一秒的时间> testA 完成， testB 只需等待。

此外，你应该写 setTimeout（testB，1000）而不是 setTimeout（'testB（）'，1000）。发送一个字符串到setTimeout就像使用 eval 一样，<小时ef =https://stackoverflow.com/questions/86513/why-is-using-javascript-eval-function-a-bad-idea>通常被认为是邪恶的并会让你成为敌人;）

Also, you should write setTimeout(testB, 1000) rather than setTimeout('testB()', 1000). Sending a string to setTimeout is, like using eval, generally considered evil and will make you enemies ;)

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