@stdlib/string-starts-with NPM

startsWith

Test if a string starts with the characters of another string.

Installation

npm install @stdlib/string-starts-with

Usage

var startsWith = require( '@stdlib/string-starts-with' );

startsWith( str, search[, position] )

Tests if a string starts with the characters of another string.

var str = 'To be, or not to be, that is the question.';

var bool = startsWith( str, 'To be' );
// returns true

bool = startsWith( str, 'to be' );
// returns false

By default, the function searches from the beginning of the input string. To search from a different character index, provide a position value (zero-based). If provided a negative position, the start index is determined relative to the string end (i.e., pos = str.length + position).

var str = 'Remember the story I used to tell you when you were a boy?';

var bool = startsWith( str, 'the story' );
// returns false

bool = startsWith( str, 'the story', 9 );
// returns true

bool = startsWith( str, 'you', -15 );
// returns true

If provided an empty search string, the function always returns true.

var str = 'beep boop';

var bool = startsWith( str, '' );
// returns true

Notes

This function differs from String.prototype.startsWith in the following ways:
- The function requires string values for the first and second arguments and requires that the position argument be an integer value.
- The function does not clamp negative position values. Instead, when provided a negative position, the function resolves the starting search position relative to the end of the string.
- Except when provided an empty search string, the function always returns false if a position resolves to a starting search position which exceeds the bounds of the input string.

Examples

var startsWith = require( '@stdlib/string-starts-with' );

var str = 'Fair is foul, and foul is fair, hover through fog and filthy air';

var bool = startsWith( str, 'Fair' );
// returns true

bool = startsWith( str, 'fair' );
// returns false

bool = startsWith( str, 'foul', 8 );
// returns true

bool = startsWith( str, 'filthy', -10 );
// returns true

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.