How to return an array of lines from a file in node.js ?

In this article, we will return an array of lines from a specified file using node.js. The fs module is used to deal with the file system in node.js and to read file data we use fs.readFileSync( ) or fs.readFile( ) methods. Here we will use the readFileSync method to read the file, and we use the steps below to return the lines of the file in an array:

Using fs.readFileSync and split method

To return an array of lines from a file in Node.js, we will

• Read the data of the file using the fs.readFileSync method, you will get a Buffer
• Convert the Buffer into a string Using the toString( ) method
• Now use the String.split() method to break the data and the delimiter should be "\n"

Example:

Below is the Example in which we are implementing the above steps:

// Requiring the fs module
const fs = require("fs")

// Creating a function which takes a file as input
const readFileLines = filename =>
  fs
    .readFileSync(filename)
    .toString('UTF8')
    .split('\n');


// Driver code
let arr = readFileLines('gfg.txt');

// Print the array
console.log(arr); 

Text file: The gfg.txt file.

Geeksforgeeks
A computer Science Portal for Geeks

Steps to Run the Code: use the following the command

node index.js

Output:

[
  'Geeksforgeeks',
  'A computer Science Portal for Geeks'
]

Using readline for Large Files

This approach uses the readline module to read a file line-by-line, storing each line in an array, which is then returned via a callback function once the file reading is complete.

Example:

// Requiring the fs and readline modules
const fs = require("fs");
const readline = require("readline");

// Creating a function which takes a file as input
const readFileLinesReadline = (filename, callback) => {
  const lines = [];
  const readInterface = readline.createInterface({
    input: fs.createReadStream(filename),
    output: process.stdout,
    console: false
  });

  readInterface.on('line', (line) => {
    lines.push(line);
  });

  readInterface.on('close', () => {
    callback(null, lines);
  });

  readInterface.on('error', (err) => {
    callback(err);
  });
};

// Driver code
readFileLinesReadline('gfg.txt', (err, arrReadline) => {
  if (err) {
    console.error(err);
    return;
  }
  // Print the array
  console.log(arrReadline);
});

Output:

[
  'Geeksforgeeks',
  'A computer Science Portal for Geeks'
]