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Standard Callback Pattern in Node Js

Filed under: NodeJs on 2024-02-22 20:46:50

AIM: To demonstrate the use of Standard callback pattern 

Objective: Node js callback pattern function callback 

Theory: Callback is an asynchronous equivalent for a function. A callback function is called at the completion of a given task. Node makes heavy use of callbacks. All the APIs of Node are written in such a way that they support callbacks. 

For example, a function to read a file may start reading file and return the control to the execution environment immediately so that the next instruction can be executed. 

Explanation: Once file I/O is complete, it will call the callback function while passing the callback function, the content of the file as a parameter. So there is no blocking or wait for File I/O. This makes Node.js highly scalable, as it can process a high number of requests without waiting for any function to return results. Create a text file named input.txt with the following content :

Create a js file named main.js with the following code :

var fs = require("fs");
var data = fs.readFileSync('input.txt');
console.log("Program Ended");

Now run the main.js to see the result −
$ node main.js
Verify the Output.

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