Open In App
Related Articles

How to Read a File Line by Line using Node.js ?

Improve
Improve
Improve
Like Article
Like
Save Article
Save
Report issue
Report

The ability to Read a File Line by Line allows us to read large files without entirely storing them in memory. It is useful in saving resources and improving the efficiency of the application. It allows us to look for the information that is required and once the relevant information is found, we can stop the search process and can prevent unwanted memory usage. We will achieve the target by using the Readline Module and Line-Reader Module.

Read a File Line by Line using the Readline Module

Readline is a native module of Node.js, it was developed specifically for reading the content line by line from any readable stream. It can be used to read data from the command line. Since the module is the native module of Node.js, it doesn’t require any installation and can be imported as –

const readline = require('readline');

Since the readline module works only with Readable streams, we need to first create a readable stream using the fs module.

const file = readline.createInterface({
input: fs.createReadStream('source_to_file'),
output: process.stdout,
terminal: false
});

Now, listen for the line event on the file object. The event will trigger whenever a new line is read from the stream:

file.on('line', (line) => {
console.log(line);
});

Example:

javascript

// Importing the Required Modules
const fs = require('fs');
const readline = require('readline');
  
// Creating a readable stream from file
// readline module reads line by line 
// but from a readable stream only.
const file = readline.createInterface({
    input: fs.createReadStream('gfg.txt'),
    output: process.stdout,
    terminal: false
});
  
// Printing the content of file line by
//  line to console by listening on the
// line event which will triggered
// whenever a new line is read from
// the stream
file.on('line', (line) => {
    console.log(line);
});

                    

Output:

Read file with Readline Module

Read a File Line by Line using Line-reader Module

The line-reader module is an open-source module for reading file line by line in Node.js. It is not the native module, so you need to install it using npm(Node Package Manager) using the command:

npm install line-reader --save

The line-reader module provides eachLine() method which reads the file line by line. It had got a callback function which got two arguments: the line content and a boolean value that stores, whether the line read, was the last line of the file.

const lineReader = require('line-reader');

lineReader.eachLine('source-to-file', (line, last) => {
console.log(line);
});

Example:

javascript

// Importing required libraries
const lineReader = require('line-reader');
  
// eachLine() method call on gfg.txt
// It got a callback function
// Printing content of file line by line
// on the console
lineReader.eachLine('gfg.txt', (line, last) => {
    console.log(line);
});

                    

Output:

Read file with Line-reader Module

Last Updated : 28 Dec, 2023
Like Article
Save Article
Previous
Next
Share your thoughts in the comments
Similar Reads