xregexp

xregexp (GitHub: slevithan/xregexp, License: MIT) provides augmented and extensible JavaScript regular expressions. You get new syntax, flags, and methods beyond what browsers support natively. XRegExp is also a regex utility belt with tools to make your client-side grepping simpler and more powerful, while freeing you from worrying about pesky cross-browser inconsistencies and the dubious lastIndex property.

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npm install xregexp

Usage examples

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// Using named capture and flag x (free-spacing and line comments)
var date = XRegExp('(?<year>  [0-9]{4} ) -?  # year  n
                    (?<month> [0-9]{2} ) -?  # month n
                    (?<day>   [0-9]{2} )     # day   ''x');
// XRegExp.exec gives you named backreferences on the match result
var match = XRegExp.exec('2012-02-22', date);
match.year; // -> '2012'
// It also includes optional pos and sticky arguments
var pos = 3, result = [];
while (match = XRegExp.exec('<1><2><3><4>5<6>', /<(d+)>/, pos, 'sticky')) {
  result.push(match[1]);
  pos = match.index + match[0].length;
// result -> ['2', '3', '4']
// XRegExp.replace allows named backreferences in replacements
XRegExp.replace('2012-02-22', date, '${month}/${day}/${year}'); // -> '02/22/2012'
XRegExp.replace('2012-02-22', date, function(match) {
  return match.month + '/' + match.day + '/' + match.year;
}); // -> '02/22/2012'

Addons

Addons are one of the more impressive features of xregexp. In particular, the matchRecursive addon allows you to match balanced brackets and quotes, which is otherwise impossible with regular regex (.NET had this extension built in for some time now however).

In browsers, first include the script:

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<script src="src/xregexp.js"></script>
<script src="src/addons/matchrecursive.js"></script>

You can then match recursive constructs using XRegExp pattern strings as left and right delimiters:

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var str = '(t((e))s)t()(ing)';
XRegExp.matchRecursive(str, '('')''g');
// -> ['t((e))s', '', 'ing']
// Extended information mode with valueNames
str = 'Here is <div> <div>an</div></div> example';
XRegExp.matchRecursive(str, '<divs*>''</div>''gi', {
    valueNames: ['between''left''match''right']
});
/* -> [
{name: 'between', value: 'Here is ',       start: 0,  end: 8},
{name: 'left',    value: '<div>',          start: 8,  end: 13},
{name: 'match',   value: ' <div>an</div>', start: 13, end: 27},
{name: 'right',   value: '</div>',         start: 27, end: 33},
{name: 'between', value: ' example',       start: 33, end: 41}
] */
// Omitting unneeded parts with null valueNames, and using escapeChar
str = '...{1}{{function(x,y){return y+x;}}';
XRegExp.matchRecursive(str, '{''}''g', {
    valueNames: ['literal'null'value'null],
    escapeChar: ''
});
/* -> [
{name: 'literal', value: '...', start: 0, end: 3},
{name: 'value',   value: '1',   start: 4, end: 5},
{name: 'literal', value: '{', start: 6, end: 8},
{name: 'value',   value: 'function(x,y){return y+x;}', start: 9, end: 35}
] */
// Sticky mode via flag y
str = '<1><<<2>>><3>4<5>';
XRegExp.matchRecursive(str, '<''>''gy');
// -> ['1', '<<2>>', '3']

XRegExp.matchRecursive throws an error if it scans past an unbalanced delimiter in the target string.

I’ve been using xregexp in syntaxhighlighter (GitHub: alexgorbatchev/SyntaxHighlighter, License: MIT LGPL) for a while now. My favourite feature is named captures, which JavaScript is desperately missing. Have you used xregexp already? How?

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nak

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