由网友(舔奶盖的小仙女)分享简介：嗯，我是新来的JavaScript和听到它是单线程的。在我的脑海里，如果你做一个异步请求，就应该启动一个自己的线程控制，如果服务器已经响应。这将不会在Javascript工作。我想有一些既节约了所有的听众，并呼吁他们，根据他们同意的条件内置机制（onreadystatechange的）。Well, i am new...

嗯，我是新来的JavaScript和听到它是单线程的。在我的脑海里，如果你做一个异步请求，就应该启动一个自己的线程控制，如果服务器已经响应。这将不会在Javascript工作。我想有一些既节约了所有的听众，并呼吁他们，根据他们同意的条件内置机制（onreadystatechange的）。

Well, i am new to javascript and heard it is single-threaded. In my mind if you make an asynchronous request, it should start an own thread which controls if the server already responded. This won't work in Javascript. I am thinking is there some built-in mechanism which saves all listeners and calls them, depending on conditions they have "agreed" to (onreadystatechange).

这只是一个假设，我想我是完全错误的。好吧，也许有人可以帮助我在这里？

This is just an assumption and I guess i am totally wrong. Well, maybe somebody can help me here?

推荐答案

只有JavaScript执行本身是单线程的，按如下说明 。然而，底层引擎可能会使用多个线程。

Only the javascript execution itself is single-threaded, as explained here. Yet, the underlying engine might use more threads.

那么，HTTP请求（在浏览器中的大便产生的地方深）可能有自己的线程，但是当事情（如响应）发生时，它会触发一个事件排队，到JS任务调度。一旦当前脚本的执行已经结束，的onreadystatechange 函数将被调用。

So, the HTTP request (created somewhere deep in the bowels of the browser) might have its own thread, but when something (like a response) happens, it will fire an event to be queued into the JS task scheduler. As soon as the current script execution has ended, the onreadystatechange function will be called.