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This article mainly explains "the meaning of async and the method of JavaScript asynchronous programming". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn the meaning of asynchronism and the method of JavaScript asynchronous programming.

What is async?

The so-called "asynchronous" means that a task is divided into two segments, first execute the first paragraph, then turn to other tasks, and then go back to the second paragraph when you are ready. This kind of discontinuous execution is called asynchronous, and the program runs asynchronously, which can improve the efficiency of program running. accordingly, continuous execution is called synchronization.

JavaScript asynchronous programming method

1. Callback function. Callback functions are very common in Javascript and can be used when you need to perform an operation after a time-consuming operation. When the number of nesting layers of the callback function is not deep, the code is easy to understand and maintain. once the number of nesting layers is deepened, there will be the problem of "callback pyramid". Another problem is that we cannot catch exceptions in the callback function outside the callback function.

2. Event monitoring (event publish / subscribe). Event monitoring is a very common asynchronous programming mode, it is a typical logic separation method, which is very suitable for some scenarios that require a high degree of decoupling. In general, we need to consider which parts are immutable and which are easy to change, encapsulate the immutable parts inside the component for external calls, and expose the customized parts to external processing. In a sense, the design of events is the interface design of components.

3. Promise object. The Promise object is natively provided in ES 6, and the Promise object represents an event (usually an asynchronous operation) that will know the result in the future, and this event provides a unified API for further processing. Using Promise object, asynchronous operation can be expressed by synchronous operation flow writing, which avoids layer upon layer of nested asynchronous callback, and the code is more clear and easy to maintain.

The asynchronous processing method of Javascript is not really asynchronous. Javascript async is implemented by event-driven. Javascript on the browser side implements two very important API, which are timers and ajax requests. If you want to know more about JavaScript asynchronous programming, you can choose professional system learning, so that your system can quickly learn technology, can enter the workplace with a high starting point.

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