如何既JS非阻塞/异步但单线程？ [英] How is JS both non-blocking / asynchronous but single-threaded?
问题描述
我有麻烦的JavaScript可视化如何既可以是单线程的，但在客户端上无阻塞。我总是想象像一条流水线：
I'm having trouble visualizing how Javascript can be both single-threaded but non-blocking on the client. I've always envisioned something like an assembly line:
-
在你的code开始执行时，你有一个单一的组装线放在一起的不同部件的汽车。
At the start of your code execution, you've got a single assembly line putting together different parts to a car.
我们得到一个点，在20％的-to-完成，其中的发动机需要被添加，但发动机尚未组装还
We get to a point at 20%-to-completion where an engine needs to be added, but an engine hasn't been assembled yet.
而不是等待发动机进行组装，组装线被分成两个组装线 - ？两个线程，右
Instead of waiting for the engine to be assembled, the assembly line gets broken up into two assembly lines - two threads, right?
1号线将继续组装汽车的其他部分。
Line 1 continues to assemble the other parts of the car.
2号线开始装配引擎。
Line 2 starts to assemble the engine.
在第2行结束该发动机的组装，它会返回到1号线和添加发动机。
When Line 2 finishes the assembly of the engine, it goes back into Line 1 and the engine is added.
-to-完成，99％-to-完成等在这一点取决于发动机是如何快速组装线1可以在30％的
Line 1 could be at 30%-to-completion, 99%-to-completion, etc at this point depending on how fast the engine was assembled.
这是怎么设想的非阻塞，异步code。 1号线的主线程得到继续，而不必等待2号线完成第一突突一起。但这种流水线隐喻需要两个组装线，或两个线程，但JS是单线程的。
This is how I envisioned non-blocking, async code. The main thread of Line 1 gets to continue to chug along without having to wait for Line 2 to finish first. But this assembly line metaphor requires two assembly lines, or two threads, but JS is single-threaded.
所以现在我很困惑。
推荐答案
在短，运行时有一个事件循环，还挺模拟异步在1个线程。
在久了，我发现这个视频和文字是一个很好的解释：
的http://2014.jsconf.eu/speakers/philip-roberts-what-the-heck-is-the-event-loop-anyway.html
In short, the runtime has an event loop that kinda simulates async in 1 thread. In long, I found this video and text to be a good explanation: http://2014.jsconf.eu/speakers/philip-roberts-what-the-heck-is-the-event-loop-anyway.html
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