Append data to a file.
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> Append data to a file.
``bash`
npm install @stdlib/fs-append-file
`javascript`
var appendFile = require( '@stdlib/fs-append-file' );
#### appendFile( file, data\[, options], clbk )
Asynchronously appends data to a file.
`javascript
var join = require( 'path' ).join;
var fpath = join( __dirname, 'examples', 'fixtures', 'file.txt' );
appendFile( fpath, 'beep boop\n', onAppend );
function onAppend( error ) {
if ( error ) {
console.log( error instanceof Error );
// => false
}
}
`
The data argument may be either a string or a [Buffer][@stdlib/buffer/ctor].
`javascript
var join = require( 'path' ).join;
var string2buffer = require( '@stdlib/buffer-from-string' );
var fpath = join( __dirname, 'examples', 'fixtures', 'file.txt' );
appendFile( fpath, string2buffer( 'beep boop\n' ), onAppend );
function onAppend( error ) {
if ( error ) {
console.log( error instanceof Error );
// => false
}
}
`
The function accepts the same options and has the same defaults as [fs.appendFile()][node-fs].
#### appendFile.sync( file, data\[, options] )
Synchronously appends data to a file.
`javascript
var join = require( 'path' ).join;
var fpath = join( __dirname, 'examples', 'fixtures', 'file.txt' );
var err = appendFile.sync( fpath, 'beep boop\n' );
if ( err instanceof Error ) {
throw err;
}
`
The function accepts the same options and has the same defaults as [fs.appendFileSync()][node-fs].
- The difference between this appendFile.sync and [fs.appendFileSync()][node-fs] is that [fs.appendFileSync()][node-fs] will throw if an error is encountered (e.g., if given a non-existent directory path) and this API will return an error. Hence, the following anti-pattern
`javascript
var fs = require( 'fs' );
// Check for directory path existence to prevent an error being thrown...
if ( fs.existsSync( '/path/to' ) ) {
fs.appendFileSync( '/path/to/file.txt', 'beep boop\n' );
}
`
can be replaced by an approach which addresses existence via error handling.
`javascript
var appendFile = require( '@stdlib/fs-append-file' );
// Explicitly handle the error...
var err = appendFile.sync( '/path/to/file.txt', 'boop beep\n' );
if ( err instanceof Error ) {
// You choose what to do...
throw err;
}
`
`javascript
var join = require( 'path' ).join;
var appendFile = require( '@stdlib/fs-append-file' );
var fpath = join( __dirname, 'examples', 'fixtures', 'file.txt' );
// Synchronously append data to a file:
var error = appendFile.sync( fpath, 'beep boop\n', 'utf8' );
// Function successfully executes and returns null
console.log( error instanceof Error );
// => false
// Asynchronously append data to a file:
appendFile( fpath, 'beep boop\n', onAppend );
function onAppend( error ) {
if ( error ) {
console.error( 'Error: %s', error.message );
}
console.log( 'Success!!!' );
}
`
- [@stdlib/fs-append-file-cli][@stdlib/fs-append-file-cli]: CLI package for use as a command-line utility.
*
This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].
#### Community
[![Chat][chat-image]][chat-url]
---
See [LICENSE][stdlib-license].
Copyright © 2016-2026. The Stdlib [Authors][stdlib-authors].
[@stdlib/fs-append-file-cli]: https://www.npmjs.com/package/@stdlib/fs-append-file-cli
[npm-image]: http://img.shields.io/npm/v/@stdlib/fs-append-file.svg
[npm-url]: https://npmjs.org/package/@stdlib/fs-append-file
[test-image]: https://github.com/stdlib-js/fs-append-file/actions/workflows/test.yml/badge.svg?branch=v0.0.3
[test-url]: https://github.com/stdlib-js/fs-append-file/actions/workflows/test.yml?query=branch:v0.0.3
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/fs-append-file/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/fs-append-file?branch=main
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[chat-url]: https://stdlib.zulipchat.com
[stdlib]: https://github.com/stdlib-js/stdlib
[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
[cli-section]: https://github.com/stdlib-js/fs-append-file#cli
[cli-url]: https://github.com/stdlib-js/fs-append-file/tree/cli
[@stdlib/fs-append-file]: https://github.com/stdlib-js/fs-append-file/tree/main
[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
[deno-url]: https://github.com/stdlib-js/fs-append-file/tree/deno
[deno-readme]: https://github.com/stdlib-js/fs-append-file/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/fs-append-file/tree/umd
[umd-readme]: https://github.com/stdlib-js/fs-append-file/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/fs-append-file/tree/esm
[esm-readme]: https://github.com/stdlib-js/fs-append-file/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/fs-append-file/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/fs-append-file/main/LICENSE
[node-fs]: https://nodejs.org/api/fs.html
[@stdlib/buffer/ctor]: https://www.npmjs.com/package/@stdlib/buffer-ctor
[standard-stream]: https://en.wikipedia.org/wiki/Pipeline_%28Unix%29