@stdlib/fs-exists NPM

Exists

Test whether a path exists on the filesystem.

Installation

npm install @stdlib/fs-exists

Usage

var exists = require( '@stdlib/fs-exists' );

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( '@stdlib/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( '@stdlib/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( '@stdlib/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

var exists = require( '@stdlib/fs-exists' );

/* 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 );
    }
}

Notice

This package is part of 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, see the main project repository.