Node.js fs.readFile() Method

The fs.readFile() method is an inbuilt method which is used to read the file. This method read the entire file into 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 accept 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 other location.
• encoding: It holds the encoding of 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.
Below examples illustrate the fs.readFile() method in Node.js:
Example 1:

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');

Output: 

readFile called
undefined

Explanation: 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.
Example 2:

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);
 })

Output:

undefined

Reference: https://nodejs.org/api/fs.html#fs_fs_readfile_path_options_callback