Node JS fs.readFile() Method

The fs.readFile() method is an inbuilt method that is used to read the file. This method read the entire file into the buffer. To load the fs module we use require() method. For example: var fs = require(‘fs’);

Syntax:

fs.readFile( filename, encoding, callback_function )

Parameters: The method accepts three parameters as mentioned above and described below:  

• filename: It holds the name of the file to read or the entire path if stored at another location.
• encoding: It holds the encoding of the file. Its default value is ‘utf8’.
• callback_function: It is a callback function that is called after reading of file. It takes two parameters:
  • err: If any error occurred.
  • data: Contents of the file.

Return Value: It returns the contents/data stored in file or error if any.

Steps to Create Node JS Application:

Step 1: In the first step, we will create the new folder by using the below command in the VScode terminal.

mkdir folder-name
cd folder-name

Step 2: Initialize the NPM using the below command. Using this the package.json file will be created.

npm init -y

Project Structure:

Project Structure

Example 1: Below examples illustrate the fs.readFile() method in Node JS. The output is undefined it means the file is null. It starts reading the file and simultaneously executes the code. The function will be called once the file has been read meanwhile the ‘readFile called’ statement is printed then the contents of the file are printed.

Javascript

// Node.js program to demonstrate
// the fs.readFile() method

// Include fs module
var fs = require('fs');

// Use fs.readFile() method to read the file
fs.readFile('Demo.txt', 'utf8', function(err, data){
    // Display the file content
    console.log(data);
});

console.log('readFile called');

Step to run the Node App:

node index.js

Output: 

readFile called
undefined

Example 2: Below examples illustrate the fs.readFile() method in Node JS:

javascript

// Node.js program to demonstrate
// the fs.readFile() method

// Include fs module
var fs = require('fs');

// Use fs.readFile() method to read the file
fs.readFile('demo.txt', (err, data) => {
    console.log(data);
 })

Step to run the Node App:

node index.js

Output:

undefined