如何编写一个需要X秒钟的函数？

Question

I want to write a javascript function that takes very close to 5 seconds to run. How can I make that guarantee?

I have tried

  function wait(numSeconds) {
    var end = new Date().getMilliseconds() + numSeconds * 1000;
    while (new Date().getMilliseconds() <= end) {}
  }

but this just crashes the page.

Answer 1

You cannot freeze the page without freezing the page.

You're trying to write a function that runs for 5 seconds straight.
Javascript runs on the UI thread, so the page will be frozen whenever any code runs.

In short, you can't do that.
You need to write asynchronous code , probably by using setTimeout() .

Answer 2

您可以使用：

var t = setTimeout(function(){alert('done')},5000);

Answer 3

If you want to wait 5 seconds before doing something, use setTimeout or setInterval . Otherwise, just eating up user time is a bad idea. In fact, the browsers will interrupt your script if it takes too long to do something, which your function most certainly will do.

Answer 4

(Ignoring for the moment why you shouldn't really do this...)

The reason your code is freezing the browser is that your while condition will never become true (for numSeconds of 1 or more).

The .getMilliseconds() method returns just the milliseconds part of the date, ie, a number between 0 and 999. For numSeconds of 1 of more your end will always be greater than 999.

Try using .getTime() instead of .getMilliseconds() . Or if you don't care about supporting old browsers uses Date.now() .

Answer 5

You could just use javascripts setTimeout instead of your own wait function.

setTimeout excecutes a function after a certain amount of time.

For example:

setTimeout(function(){}, 5000);

Would just wait 5 seconds.

See more at w3schools .

Answer 6

Strictly speaking, what you ask cannot be done because, as you've seen, the page will freeze while you wait.

As a practical matter, though, I suspect that what you really want is the something like this:

function waitawhile() {
    setTimeout( function() {
        alert('5 seconds has passed');
    }, 5000);
}