Detailed explanation of JavaScript implementation of threads and event loop

This article talks about javascript Implementing threads and event loops. If you don’t know about javascript’s implementation of threads and event loops, or if you are interested in javascript’s implementation of threads and event loops, let’s take a look. This article, let’s cut the nonsense and get to the point

1. Why is JavaScript said to be single-threaded?

The several threads involved in the browser rendering process are: JavaScript execution thread, responsible for executing js code, UI thread, responsible for UI display ,JavaScript eventLoop thread, manage

Manage JavaScript events, where the JavaScript execution thread and the UI thread are mutually exclusive. If JavaScript is multi-threaded, then When multiple JavaScript execution threads operate the same DOM, such as turning a button red and yellow respectively, the UI thread will be confused. Who should listen? In order to avoid this situation in JavaScript, these

threads must be executed separately, so JavaScript is single-threaded. This has become the core feature of this language and will not be used in the future. will change.

2. JavaScript taskQueue

Structure and event loop

Single thread means , all tasks need to be queued, and the next task will not be executed until the previous task is completed. If the previous task takes a long time, the latter task will have to

keep waiting.

Execution tasks in JavaScript are executed according to the queue data structure, as shown below:

Tasks in JavaScript:

1. Synchronization tasks:

for loop, summation, js assignment, js operation, etc.##2. Asynchronous tasks: dom events, bom api processing ajax

The so-called "

Callback function

" (callback) is the code that will be hung up by the main thread. Asynchronous tasks must specify a callback function. When the main thread starts executing an asynchronous task, executes the corresponding callback function.

Loop mechanism:

The JavaScript main thread directly executes the synchronous task, the asynchronous task executes part of the asynchronous task first, and then

exits The main thread executes, Then wait for the asynchronous task to be ready before handing it over to the main thread for execution.

In short, JavaScript code is executed one by one in the form of a queue, and only one piece of code can be executed at the same time.

The above is all the content of this article. If you don’t know much about it, you can try to write some event loops, etc. This will make it easy to master!

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