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startsWith

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

Installation

npm install @stdlib/string-starts-with

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).
• To use as a general utility for the command line, install the corresponding CLI package globally.

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

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

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CLI

Installation

To use as a general utility, install the CLI package globally

npm install -g @stdlib/string-starts-with-cli

Usage

Usage: starts-with [options] --search=<string> [<string>]

Options:

  -h,    --help                Print this message.
  -V,    --version             Print the package version.
         --search string       Search string.
         --pos int             Search position.
         --split sep           Delimiter for stdin data. Default: '/\\r?\\n/'.

Notes

• If the split separator is a regular expression, ensure that the split option is either properly escaped or enclosed in quotes.

  # Not escaped...
  $ echo -n $'Hello, World!\nBeep Boop Baz' | starts-with --search=Beep --split /\r?\n/
  
  # Escaped...
  $ echo -n $'Hello, World!\nBeep Boop Baz' | starts-with --search=Beep --split /\\r?\\n/

• The implementation ignores trailing delimiters.

Examples

$ starts-with --search=be beep
true

To use as a standard stream,

$ echo -n 'boop' | starts-with --search=bo
true

By default, when used as a standard stream, the implementation assumes newline-delimited data. To specify an alternative delimiter, set the split option.

$ echo -n 'Hello, World!\tBeep Boop' | starts-with --search=Beep --split '\t'
false
true

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See Also

• @stdlib/string-ends-with: test if a string ends with the characters of another string.

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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.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2025. The Stdlib Authors.