Skip to content
Related Articles

Related Articles

Improve Article
Node.js fs.filehandle.write() Method
  • Last Updated : 09 Jul, 2020

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

Syntax:

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

Parameter: This method does 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 write.
  • 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.

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



Example 1: Filename: index.js




// 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 asyncrionise function
async function funct() {
  
    // Initializng 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+');
  
        // Writting 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




// Node.js program to demonstrate the 
// filehandle.sync() 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) => {
  
    // Cathing 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 asyncrionise function
async function funct() {
  
    // Initializng filehandle
    let filehandle = null;
  
    // Initializng following variables
    let buffer = Buffer.from('ABCD');
  
    try {
  
        // Creating and initiating  filehandle
        filehandle = await 
            fsPromises.open(file, 'r+');
  
        // Writting 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




My Personal Notes arrow_drop_up
Recommended Articles
Page :