Node Callback Concept

A callback in Node is a non-blocking function that executes upon task completion, enabling asynchronous processing. It facilitates scalability by allowing Nodejs to handle multiple requests without waiting for operations to conclude, as exemplified in file I/O scenarios.

Explanation: The fs library is used for file-system operations. The readFileSync() function is synchronous, halting program execution until completion. This blocking behavior ensures that the program reads the file before progressing further.

Example 1: Code for reading a file synchronously (blocking code) in Nodejs. Create a text file inputfile1.txt with the following content:

Hello Programmer!!!
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// Write JavaScript code
const fs = require("fs");
const filedata = fs.readFileSync('inputfile1.txt');
console.log(filedata.toString());
console.log("End of Program execution");

Output:

Explanation: The fs library is utilized for file-system operations. The asynchronous readFile() function allows the program to proceed immediately to the next instruction while the task runs in the background. A callback function is employed to execute upon the completion of the background task.

Example 2: Code for reading a file asynchronously (non-blocking code) in Nodejs. Create a text file inputfile1.txt with the following content.

Hello Programmer!!!
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// Write a JavaScript code
const fs = require("fs");

fs.readFile('inputfile1.txt',
    function (ferr, filedata) {
        if (ferr) return console.error(ferr);
        console.log(filedata.toString());
    }
);
console.log("End of Program execution");

Output: