startsWith
Test if a string starts with the characters of another string.
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.startsWithin the following ways:- The function requires string values for the first and second arguments and requires that the
positionargument be an integer value. - The function does not clamp negative
positionvalues. Instead, when provided a negativeposition, the function resolves the starting search position relative to the end of the string. - Except when provided an empty
searchstring, the function always returnsfalseif apositionresolves to a starting search position which exceeds the bounds of the input string.
- The function requires string values for the first and second arguments and requires that the
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
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
splitoption 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