Node.js fs.filehandle.truncate() Method
Last Updated :
29 Dec, 2022
The fs.filehandle.truncate() method is an inbuilt application programming interface of class fs.filehandle within File System module which is used to truncate the particular file object and only that much byte will be retained which passed as an integer in truncate() method.
Syntax:
const filehandle.truncate(len)
Parameter: This method takes the length of bytes till which this file has to be truncated.
Return value: This method returns an pending promise which contains no value in it.
Below programs illustrates the use of fs.filehandle.truncate() method in Node.js:
Example 1: Filename: index.js
Javascript
const fs = require( 'fs' );
const fsPromises = fs.promises;
async function funct() {
let filehandle = null ;
let prom = null ;
try {
console.log( "data before operation: " +
fs.readFileSync( 'example.txt' , 'utf8' ));
filehandle = await
fsPromises.open( 'example.txt' , 'r+' );
prom = filehandle.truncate(5);
} finally {
if (filehandle) {
console.log( "data after operation: " +
fs.readFileSync( 'example.txt' , 'utf8' ));
await filehandle.close();
}
}
}
funct(). catch (console.error);
|
Run index.js file using the following command:
node index.js
Output:
data before operation: ABCDEFGHIJK
data after operation: ABCDE
Example 2: Filename: index.js
Javascript
const fs = require( 'fs' );
const fsPromises = fs.promises;
let data = "This is a file containing "
+ "a collection of books." ;
let file = "books.txt" ;
fs.writeFile(file, data, (err) => {
if (err) {
console.log(err);
}
});
fs.exists(file, (exists) => {
if (exists) {
console.log(
"content of file before operation: "
+ (fs.readFileSync(file)));
}
});
async function funct() {
let filehandle = null ;
try {
filehandle = await fsPromises.open(file, 'r+' );
prom = filehandle.truncate(4);
} finally {
if (filehandle) {
console.log(
"content of file after operation: "
+ (fs.readFileSync(file)));
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.
content of file after operation: This
NOTE: The above program will not run on online JavaScript and script editor.
Reference: https://nodejs.org/dist/latest-v12.x/docs/api/fs.html#fs_filehandle_truncate_len
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