html5和javascript：setTimeout是否会打破这一点？

Question

I am confused as to why the following html is not working. 我对为什么以下html无法正常工作感到困惑。 I would expect it to keep sending alerts but it stops after one. 我希望它会继续发送警报，但是在发出警报后会停止。 Furthermore, the "left fn" alert never occurs! 而且，“ left fn”警报永远不会发生！ Can anyone explain this to me? 有人可以向我解释吗？ I am using html5 with javascript in firefox on ubuntu. 我在ubuntu上的Firefox中使用html5和javascript。

<!DOCTYPE html>
   <script>
      function alertme() {
      alert ("in fn");
      }

      while (true) {
       window.setTimeout(alertme(), 3000);
   alert("left fn");
      }
   </script>

Answer 1

while (true) {
    window.setTimeout(alertme, 3000); //setTimeout wants a function, not the return value of the function
    alert("left fn");
}

btw, have fun with klicking all the messageboxes away... 顺便说一句，快点踢掉所有的消息框...

Answer 2

A few probable issues: 一些可能的问题：

alertme() is being called immediately and its return value is instead being passed to setTimeout() . alertme()被立即调用，并且其return值被传递给setTimeout() 。
To fix this, you can pass alertme as a reference (without the calling parenthesis): 要解决此问题，您可以将alertme作为参考传递（不带调用括号）：
```
 setTimeout(alertme, 3000); 
```
However, this will then conflict with JavaScript's (primarily) single-threaded nature. 但是，这将与JavaScript的（主要）单线程性质发生冲突。
The setTimeout() s, being asynchronous, simply start a timer that expires no less than 3 seconds from now. setTimeout()是异步的，只需启动一个计时器，此计时器从现在起持续不少于 3秒钟。 But, they require that the one thread is eventually not busy for the delayed task to be performed. 但是，他们要求一个线程最终不忙于执行延迟的任务。
However, the while (true) {} , being synchronous and indefinite, will keep the thread busy until all execution is stopped and will never allow the timeouts to perform their tasks. 但是， while (true) {}是同步且不确定的，它将使线程保持忙碌状态，直到所有执行停止为止，并且永远不会允许超时执行其任务。 So, you will never see "in fn" . 因此，您将永远不会看到"in fn" 。
John Resig has a good write up on timers: http://ejohn.org/blog/how-javascript-timers-work/ John Resig在计时器方面写得很好： http : //ejohn.org/blog/how-javascript-timers-work/

How exactly to fix the code depends on the intent. 如何精确地修复代码取决于意图。

html5和javascript：setTimeout是否会打破这一点？

问题描述

2 个解决方案

解决方案1
2 2013-02-19 23:47:19

解决方案2
2 已采纳 2013-02-19 23:56:25

html5和javascript：setTimeout是否会打破这一点？

问题描述

2 个解决方案

解决方案1 2 2013-02-19 23:47:19

解决方案2 2 已采纳 2013-02-19 23:56:25

解决方案1
2 2013-02-19 23:47:19

解决方案2
2 已采纳 2013-02-19 23:56:25