String.prototype.extract

14 Jul 2009

I recently released some useful additions to String.prototype over on Github (linky). One of the more useful methods in there is extract. I’m sure something similar to this already exists but I’ve yet to find it.

It’s useful when you need to extract a particular group of every match from a global regular expression. Normally you’d have to use the RegExp.exec method along with a while loop to extract that info, and, that is exactly what’s going on behind the scenes. Have a look:

The code:

String.prototype.extract = function( regex, n ) {
 
    n = n === undefined ? 0 : n;
 
    if ( !regex.global ) {
        return this.match(regex)[n] || '';
    }
 
    var match,
        extracted = [];
 
    while ( (match = regex.exec(this)) ) {
        extracted[extracted.length] = match[n] || '';
    }
 
    return extracted;
 
};

Example:

('hi @rob and @adam, oh and @bob').extract(/@(w+)/g, 1);
    // => ['rob', 'adam', 'bob']

(With the above example, you could achieve it with a simple match() if JavaScript supported look-behinds…)

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So far there's been 2 Responses to
“String.prototype.extract”

Pete July 14th, 2009 at 1:30 pm

I did this recently, which is sort of the reverse of your extract method

String.prototype.bindData = function ( str, data ) {
  var m;
  while ( m = /%{s*([^}s]+)s*}/.exec(str) ) {
    str = str.replace( m[0], data[m[1]] || '??' );
  }
  return str;
};
 
 
// Example
 
var data = {
    'brown': 'red',
    'lazy': 'slow'
  };
 
"The quick %{brown} fox jumped over the %{lazy} dog".bindData( data );
// The quick red fox jumped over the slow dog

John.H July 17th, 2009 at 10:48 am

hi,Pete, I think there is something wrong in your code, so I just modified it and it works now:

String.prototype.bindData = function (data) {
  var m,ret = this;
  while ( m = /%{s*([^}s]+)s*}/.exec(ret) ) {
    ret = ret.replace( m[0], data[m[1]] || '??' );
  }
  return ret;
};