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About stdlib...

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.

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.

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.

To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

Exists

NPM version Build Status Coverage Status

Test whether a path exists on the filesystem.

Usage

import exists from 'https://cdn.jsdelivr.net/gh/stdlib-js/fs-exists@esm/index.mjs';

You can also import the following named exports from the package:

import { sync } from 'https://cdn.jsdelivr.net/gh/stdlib-js/fs-exists@esm/index.mjs';

exists( path, clbk )

Asynchronously tests whether a path exists on the filesystem.

exists( __dirname, done );

function done( bool ) {
    if ( bool ) {
        console.log( '...path exists.' );
    } else {
        console.log( '...path does not exist.' );
    }
}

The above callback signature matches the now deprecated fs.exists() API. The function also accepts the more conventional error-first style callback signature found in most asynchronous Node APIs.

exists( __dirname, done );

function done( error, bool ) {
    if ( error ) {
        console.error( error.message );
    }
    if ( bool ) {
        console.log( '...path exists.' );
    } else {
        console.log( '...path does not exist.' );
    }
}

exists.sync( path )

Synchronously tests whether a path exists on the filesystem.

var bool = exists.sync( __dirname );
// returns <boolean>

Notes

  • The following is considered an anti-pattern:

    var path = require( 'path' );
var readFileSync = require( 'https://cdn.jsdelivr.net/gh/stdlib-js/fs-read-file' ).sync;

var file = path.join( __dirname, 'foo.js' );
if ( exists.sync( __dirname ) ) {
    file = readFileSync( file );
}

    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.

    Instead, the following pattern is preferred, where errors are handled explicitly:

    var path = require( 'path' );
var readFileSync = require( 'https://cdn.jsdelivr.net/gh/stdlib-js/fs-read-file' ).sync;

var file = path.join( __dirname, 'foo.js' );
try {
    file = readFileSync( file );
} catch ( error ) {
    console.log( 'unable to read file.' );
    console.error( error );
}

  • Nevertheless, use cases exist where one desires to check existence without performing IO. For example,

    var path = require( 'path' );
var writeFileSync = require( 'https://cdn.jsdelivr.net/gh/stdlib-js/fs-write-file' ).sync;

var file = path.join( __dirname, 'foo.js' );
if ( exists.sync( file ) ) {
    console.log( 'Don\'t overwrite the file!' );
} else {
    writeFileSync( file, 'beep', {
        'encoding': 'utf8'
    });
}

Examples

<!DOCTYPE html>
<html lang="en">
<body>
<script type="module">

import exists from 'https://cdn.jsdelivr.net/gh/stdlib-js/fs-exists@esm/index.mjs';

/* Sync */

console.log( exists.sync( __dirname ) );
// => true

console.log( exists.sync( 'beepboop' ) );
// => false

/* Async */

exists( __dirname, done );
exists( 'beepboop', done );

function done( error, bool ) {
    if ( error ) {
        console.error( error.message );
    } else {
        console.log( bool );
    }
}

</script>
</body>
</html>

See Also

Notice

This package is part of stdlib, a standard library 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, see the main project repository.

Community

Chat

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.