Node.js fs.filehandle.write() Method

The fs.filehandle.write() method is an inbuilt application programming interface of class fs.filehandle within the File System module which is used to write the data from the buffer to that particular file.

Syntax:

const filehandle.write(buffer[, offset[, length[, position]]])

Parameter: This method takes the following parameter:  

• buffer: Buffer which will provide the data that need to be stored.
• offset: Start point in the buffer.
• length: Number of bytes to be written.
• position: Start point of the file.

Return value: This method returns a pending promise which contains buffer and bytesWritten property which describes the number of bytes written.

The below programs illustrates the use of fs.filehandle.write() method in Node.js:

Example 1: Filename: index.js

javascript

// Node.js program to demonstrate the
// filehandle.write() method
const fs = require('fs');
const fsPromises = fs.promises;

console.log("file before write operation :- "
    + fs.readFileSync('example.txt', 'utf8'));

// Initiating asynchronise function
async function funct() {

    // Initializing following variables
    let filehandle = null;
    let prom = null;
    let buffer = Buffer.from('Geeks');

    try {

        // Creating and initiating filehandle
        filehandle = await
            fsPromises.open('example.txt', 'r+');

        // Writing the file by using
        // write() method
        prom = filehandle.write(
            buffer, 0, buffer.length, 0);

    } finally {

        if (filehandle) {

            // Display the result
            prom.then(function (result) {
                console.log(
                    "file after write operation :- "
                    + (result.buffer).toString());
            })

            // Close the file if it is opened.
            await filehandle.close();
        }
    }
}

funct().catch(console.error);

Directory structure before running the program: 

Directory structure after running the program: 

Run index.js file using the following command: 

node index.js

Output:

file before write operation :- Geeks for Geeks
file after write operation :- Geeks

Example 2: Filename: index.js

javascript

// Node.js program to demonstrate the
// filehandle.write() method
const fs = require('fs');
const fsPromises = fs.promises;

// Data for the new file
let data = "This is a file containing"
    + " a collection of books.";

// Name of the file to be created
let file = "books.txt";

// Creating the new file 'books.txt'
fs.writeFile(file, data, (err) => {

    // Catching error
    if (err) {
        console.log(err);
    }
});

// Using fs.exists() method
fs.exists(file, (exists) => {
    if (exists) {
        console.log(
            "content of file before operation :- "
            + (fs.readFileSync(file)));
    }
});

// Initiating asynchronise function
async function funct() {

    // Initializing filehandle
    let filehandle = null;

    // Initializing following variables
    let buffer = Buffer.from('ABCD');

    try {

        // Creating and initiating  filehandle
        filehandle = await
            fsPromises.open(file, 'r+');

        // Writing the file
        // by using write() method
        prom = filehandle.write(
            buffer, 0, buffer.length, 0);

    } finally {

        if (filehandle) {

            // Display the result
            prom.then(function (result) {
                console.log(
                    "file after write operation :- "
                    + (result.buffer).toString());
            })

            await filehandle.close();
        }
    }
}

funct().catch(console.error);

Directory structure before running the program: 

Directory structure after running the program: 

Run index.js file using the following command: 

node index.js

Output: 

content of file before operation :- 
  This is a file containing a collection of books.
file after write operation :- ABCD

Reference: https://nodejs.org/dist/latest-v12.x/docs/api/fs.html#fs_filehandle_write_buffer_offset_length_position