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This article focuses on "how to use the callback function in Node.js". Interested friends may wish to take a look at it. The method introduced in this paper is simple, fast and practical. Now let the editor take you to learn how to use the callback function in Node.js.

Interesting talk about callback function of Node.js

The direct embodiment of Node.js asynchronous programming is the callback function, which will be called after completing the task, while Node.js uses a large number of callback functions. I think it is appropriate to use Node.js to talk about callback functions. Next, I will try my best to talk about callback functions. [recommended study: "nodejs tutorial"]

What is a callback function?

You go to the online forum to find the resource seed, but the resource you are looking for can not be found, so you post in the forum and leave an email to ask for the resource. After a few days, some netizens found the resource and sent you an email. Then you received the resource seed and went to download the resource. Here, you leave your mailbox in the forum to register the callback function, and the mailbox you leave is the callback function. Someone finds the resource and sends you an email that triggers the callback function and calls the callback function. You get the seed and download it to respond to the callback event.

Example:

Function main (info,callback) {console.log ("like, comment, retweet?!") Callback (info)} function say (msg) {console.log (msg)} main ("Yes, yes!" , say)

Here callback is the callback function, and of course you don't have to use that name. In the function body, you output a piece of information before calling the callback function, and the (callback) callback function takes msg as its argument.

Callback function example

There are two ways to read a file using a Node.js program. One is a synchronous operation, which allows subsequent commands to be executed only after the read operation is completed, which is called blocking. Another way is asynchronous, which can read files and execute other commands at the same time, which is also called non-blocking.

The non-blocking method is based on callback functions and allows operations to be performed in parallel. The result of the operation is handled by the callback function when the event occurs, so the program does not have to wait for the result of an operation to perform the next step, which greatly improves the performance of Node.js and enables it to handle a large number of concurrent requests.

For example:

Const fs = require ("fs") fs.readFile ('. / foo.txt',function (err,data) {if (err) return console.error (err) console.log (data.toString ())}) console.log ("Node.js program has been executed ~")

Running result:

The Node.js program has been executed. Little ones, please give me a like.

You can find that when reading a file, the following output statement is executed regardless of whether the file has been read or not. Therefore, the words that the program has ended are displayed first, and then wait for the file to be read and then the contents of the file are displayed. The contents of the file are returned as an argument to the callback function, data, so you don't have to wait for the file Icano to finish executing the code.

At this point, I believe you have a deeper understanding of "how to use the callback function in Node.js". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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