npm package: @stdlib/fs-append-file
Description: Append data to a file.
Author: The Stdlib Authors
Latest version: 0.0.3

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<details>
  <summary>
    About stdlib...
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</details>

# Append File

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

> Append data to a file.

<section class="installation">

## Installation

```bash
npm install @stdlib/fs-append-file
```

</section>

<section class="usage">

## Usage

```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].

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   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

    <!-- eslint-disable node/no-sync -->

    ```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.

    <!-- eslint-disable node/no-sync -->

    ```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;
    }
    ```

</section>

<!-- /.notes -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```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!!!' );
}
```

</section>

<!-- /.examples -->



<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

## See Also

-   <span class="package-name">[`@stdlib/fs-append-file-cli`][@stdlib/fs-append-file-cli]</span><span class="delimiter">: </span><span class="description">CLI package for use as a command-line utility.</span>


</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->


<section class="main-repo" >

* * *

## Notice

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]

---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

</section>

<!-- /.stdlib -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="links">

[@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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[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

</section>

<!-- /.links -->