Node.js fs.filehandle.datasync() Method

Last Updated : 29 Dec, 2022

The fs.filehandle.datasync() method is an inbuilt application programming interface of class fs.filehandle within File System module which is used to sync the data of the file.

Syntax:

const filehandle.datasync()

Parameter: This method does not accept any parameter.
Return value: This method returns an pending promise which contain no value in it.

Below programs illustrates the use of fs.filehandle.datasync() method.

Example 1: Filename: index.js

JavaScript

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

console.log("File content before operation: "
        + (fs.readFileSync('example.txt')));

// Initiating asynchronise function
async function funct() {

    // Initializing filehandle
    let filehandle = null;

    try {

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

        // Syncing the data by using
        // datasync() method
        await filehandle.datasync();

    } finally {

        if (filehandle) {

            // Close the file if it is opened.
            console.log("data synced successfully");
            console.log("Content after operation: "
                + (fs.readFileSync('example.txt')));

            await filehandle.close();
        }
    }
}

funct().catch(console.error);

Directory structure of the program:

Run index.js file using the following command:

node index.js

Output:

File content before operation: Content of the example.txt file
data synced successfully
Content after operation: Content of the example.txt file

Example 2: Filename: index.js

JavaScript

// Node.js program to demonstrate the 
// filehandle.datasync() 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;

    try {

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

        // Syncing the data by using 
        // datasync() method
        await filehandle.datasync();

    } finally {

        if (filehandle) {

            // Close the file if it is opened.
            console.log("data synced successfully");
            console.log("content of file after"
                + " operation: " + 
                (fs.readFileSync(file)));

            await filehandle.close();
        }
    }
}

funct().catch(console.error);

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.
data synced successfully
content of file after operation: This is a file containing a collection of books.

Directory structure before running the program:

Directory structure after running the program: