Node Callback Concept

In Node.js, callbacks enable asynchronous, non-blocking execution, while methods like readFileSync() perform blocking operations. The fs module provides both synchronous and asynchronous approaches to handle file system tasks.

Callback Function: Executes after a task completes, enabling non-blocking processing.
Improves Scalability: Allows handling multiple requests without waiting for operations to finish.
readFileSync(): A synchronous method that blocks execution until the file is fully read.
Asynchronous Methods: Continue execution while file operations run in the background.

Example: 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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JavaScript

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

Output:

The fs library is used to perform file system operations in Node.js.
The asynchronous readFile() function allows the program to continue execution while the file is being read in the background.
A callback function is executed after the file-reading operation is completed.

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

Hello Programmer!!!
Learn NodeJS with GeeksforGeeks

JavaScript

// 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:

The fs.readFile() function reads the file asynchronously (non-blocking).
The program does not wait for the file to be read.
"End of Program execution" is printed first.
The file content is printed later when the callback runs.

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