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Node.js fs.filehandle.datasync() Method

  • Last Updated : 09 Jul, 2021

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 asyncrionise 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) => {
 
    // 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() {
 
    // 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: 
 

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




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