Node.js fs.writeSync() Method

The file system module or fs module is an inbuilt module in Node js which is used to work with files on the computer. The functions of the module can be used by importing the fs module. The fs module can be included in the program by using the fs.writeSync() function of the filesystem module is the synchronous version of the write() method. It can be used for writing text as well as binary data onto the file. 

Syntax:

fs.writeSync( fd, string, position, encoding )

fs.writeSync( fd, buffer, offset, length, position )

Parameters:

• fd: It stands for file descriptor which is a number that identifies the file. We can use fs.openSync() method and pass a string within it describing the location of the file and it will return an integer which is the file descriptor.
• string: It is a string that will be written onto the file.
• position: It specifies the position in the file where the text will be written. If the position is not passed in the method or an integer value is not used for specifying position then it will start writing from the 0^th position. If a string is already written on that position the method will overwrite the new string passed on that position.
• encoding: It is a string that specifies character encoding. By default it is utf8.
• buffer: It contains the buffer type value like Buffer, Typed Array, Data View.
• offset: It is an integer value that specifies the part of the buffer to be written on the file.
• length: It is an integer value that specifies the number of bytes to write into the file.

Return value: Number of bytes written is returned.

Example:

// Importe fs module
const fs = require("fs");

// Create a file input.txt and open it
// using openSync
// The second parameter is the flag 
// which is r+ used for reading and 
// writing onto the file
// An exception occurs if the file does
// not exist.
// The method returns an integer which
// is the file descriptor fd
const fd = fs.openSync("input.txt", "r+");

// This text will be written on file input.text
const text = "Welcome to GeeksforGeeks";

// Starting position in file
const position = 0;

// writeSync returns number of bytes written
// on file which is stores in this variable
const numberOfBytesWritten = 
    fs.writeSync(fd, text, position, 'utf8');

console.log('File written successfully using writeSync()');

console.log(`Text written on file: ${text},
        starting from position: ${position}`);

console.log(`Number of Bytes written: 
        ${numberOfBytesWritten}`);

Run index.js file using below command:

node index.js

Console Output:

File written successfully using writeSync()
Text written on file: Welcome to GeeksforGeeks,starting from position: 0
Number of Bytes written: 24

Example:

// Importing fs module
const fs = require("fs");

// open file using openSync in writing mode
// The file is created if it does not exist
// or truncated if it exists
// The method returns an integer which is
// the file descriptor fd
const fd = fs.openSync("binaryFile", "w");


// Create a buffer which will be written
// onto the file
const buffer = new Buffer.from(
    'GeeksforGeeks: A computer science portal for geeks');

// Starting position in file
const position = 0;

// writeSync returns number of bytes written
// on file which is stores in this variable
const numberOfBytesWritten = 
    fs.writeSync(fd, buffer, position, 50);

console.log('File written successfully using writeSync()');

console.log(`Buffer written on file: ${buffer},
            starting from position: ${position}`);

console.log(`Number of Bytes written: 
            ${numberOfBytesWritten}`);

Run index.js file using below command:

node index.js

Console Output:

File written successfully using writeSync()
Buffer written on file: GeeksforGeeks: A computer science portal for geeks
starting from position: 0
Number of Bytes written: 50

Reference:

• https://nodejs.org/api/fs.html#fs_fs_writesync_fd_string_position_encoding
• https://nodejs.org/api/fs.html#fs_fs_writesync_fd_buffer_offset_length_position