299 lines
8.9 KiB
Markdown
299 lines
8.9 KiB
Markdown
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<!--
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@license Apache-2.0
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Copyright (c) 2018 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<details>
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<summary>
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About stdlib...
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</summary>
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<p>We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.</p>
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<p>The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.</p>
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<p>When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.</p>
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<p>To join us in bringing numerical computing to the web, get started by checking us out on <a href="https://github.com/stdlib-js/stdlib">GitHub</a>, and please consider <a href="https://opencollective.com/stdlib">financially supporting stdlib</a>. We greatly appreciate your continued support!</p>
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</details>
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# Exists
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[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->
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> Test whether a path exists on the filesystem.
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<section class="installation">
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## Installation
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```bash
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npm install @stdlib/fs-exists
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```
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</section>
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<section class="usage">
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## Usage
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```javascript
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var exists = require( '@stdlib/fs-exists' );
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```
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#### exists( path, clbk )
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Asynchronously tests whether a path exists on the filesystem.
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```javascript
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exists( __dirname, done );
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function done( bool ) {
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if ( bool ) {
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console.log( '...path exists.' );
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} else {
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console.log( '...path does not exist.' );
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}
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}
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```
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The above callback signature matches the now **deprecated** [`fs.exists()`][node-fs-exists] API. The function also accepts the more conventional `error`-first style callback signature found in most asynchronous Node APIs.
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```javascript
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exists( __dirname, done );
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function done( error, bool ) {
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if ( error ) {
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console.error( error.message );
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}
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if ( bool ) {
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console.log( '...path exists.' );
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} else {
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console.log( '...path does not exist.' );
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}
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}
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```
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#### exists.sync( path )
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Synchronously tests whether a path exists on the filesystem.
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```javascript
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var bool = exists.sync( __dirname );
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// returns <boolean>
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- The following is considered an anti-pattern:
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```javascript
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var path = require( 'path' );
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var readFileSync = require( '@stdlib/fs-read-file' ).sync;
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var file = path.join( __dirname, 'foo.js' );
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if ( exists.sync( __dirname ) ) {
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file = readFileSync( file );
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}
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```
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Because time elapses between checking for existence and performing IO, at the time IO is performed, the path is no longer guaranteed to exist. In other words, a race condition exists between the process attempting to read and another process attempting to delete.
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Instead, the following pattern is preferred, where `errors` are handled explicitly:
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```javascript
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var path = require( 'path' );
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var readFileSync = require( '@stdlib/fs-read-file' ).sync;
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var file = path.join( __dirname, 'foo.js' );
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try {
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file = readFileSync( file );
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} catch ( error ) {
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console.log( 'unable to read file.' );
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console.error( error );
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}
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```
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- Nevertheless, use cases exist where one desires to check existence **without** performing IO. For example,
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<!-- run-disable -->
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```javascript
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var path = require( 'path' );
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var writeFileSync = require( '@stdlib/fs-write-file' ).sync;
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var file = path.join( __dirname, 'foo.js' );
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if ( exists.sync( file ) ) {
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console.log( 'Don\'t overwrite the file!' );
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} else {
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writeFileSync( file, 'beep', {
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'encoding': 'utf8'
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});
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}
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```
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</section>
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<!-- /.notes -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var exists = require( '@stdlib/fs-exists' );
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/* Sync */
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console.log( exists.sync( __dirname ) );
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// => true
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console.log( exists.sync( 'beepboop' ) );
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// => false
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/* Async */
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exists( __dirname, done );
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exists( 'beepboop', done );
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function done( error, bool ) {
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if ( error ) {
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console.error( error.message );
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} else {
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console.log( bool );
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}
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}
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```
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</section>
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<!-- /.examples -->
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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
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<section class="related">
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## See Also
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- <span class="package-name">[`@stdlib/fs-exists-cli`][@stdlib/fs-exists-cli]</span><span class="delimiter">: </span><span class="description">CLI package for use as a command-line utility.</span>
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- <span class="package-name">[`@stdlib/fs-read-file`][@stdlib/fs/read-file]</span><span class="delimiter">: </span><span class="description">read the entire contents of a file.</span>
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- <span class="package-name">[`@stdlib/fs-read-dir`][@stdlib/fs/read-dir]</span><span class="delimiter">: </span><span class="description">read the entire contents of a directory.</span>
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</section>
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<!-- /.related -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="main-repo" >
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* * *
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## Notice
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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.
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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].
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#### Community
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[![Chat][chat-image]][chat-url]
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---
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## License
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See [LICENSE][stdlib-license].
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## Copyright
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Copyright © 2016-2024. The Stdlib [Authors][stdlib-authors].
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</section>
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<!-- /.stdlib -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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[@stdlib/fs-exists-cli]: https://www.npmjs.com/package/@stdlib/fs-exists-cli
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[npm-image]: http://img.shields.io/npm/v/@stdlib/fs-exists.svg
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[npm-url]: https://npmjs.org/package/@stdlib/fs-exists
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[test-image]: https://github.com/stdlib-js/fs-exists/actions/workflows/test.yml/badge.svg?branch=v0.2.2
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[test-url]: https://github.com/stdlib-js/fs-exists/actions/workflows/test.yml?query=branch:v0.2.2
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[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/fs-exists/main.svg
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[coverage-url]: https://codecov.io/github/stdlib-js/fs-exists?branch=main
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<!--
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[dependencies-image]: https://img.shields.io/david/stdlib-js/fs-exists.svg
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[dependencies-url]: https://david-dm.org/stdlib-js/fs-exists/main
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-->
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[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg
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[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im
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[stdlib]: https://github.com/stdlib-js/stdlib
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[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
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[cli-section]: https://github.com/stdlib-js/fs-exists#cli
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[cli-url]: https://github.com/stdlib-js/fs-exists/tree/cli
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[@stdlib/fs-exists]: https://github.com/stdlib-js/fs-exists/tree/main
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[umd]: https://github.com/umdjs/umd
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[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
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[deno-url]: https://github.com/stdlib-js/fs-exists/tree/deno
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[deno-readme]: https://github.com/stdlib-js/fs-exists/blob/deno/README.md
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[umd-url]: https://github.com/stdlib-js/fs-exists/tree/umd
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[umd-readme]: https://github.com/stdlib-js/fs-exists/blob/umd/README.md
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[esm-url]: https://github.com/stdlib-js/fs-exists/tree/esm
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[esm-readme]: https://github.com/stdlib-js/fs-exists/blob/esm/README.md
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[branches-url]: https://github.com/stdlib-js/fs-exists/blob/main/branches.md
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[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/fs-exists/main/LICENSE
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[node-fs-exists]: https://nodejs.org/api/fs.html#fs_fs_exists_path_callback
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<!-- <related-links> -->
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[@stdlib/fs/read-file]: https://www.npmjs.com/package/@stdlib/fs-read-file
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[@stdlib/fs/read-dir]: https://www.npmjs.com/package/@stdlib/fs-read-dir
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<!-- </related-links> -->
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</section>
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<!-- /.links -->
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