prototype javascript library String.gsub example

<script type="text/javascript" charset="utf-8">
 function doc (argument) {
  document.write(argument);
  document.write("<br />\n");
 }

 // Ruby String.gsub
 // In the block form, the current match is passed in as a parameter, 
 // and variables such as $1, $2, $`, $&, and $' will be set appropriately. 
 // The value returned by the block will be substituted for the match on each call.
 Object.extend(String.prototype, {
   gsub: function(pattern, replacement) {
     var result = '', source = this, match;
     replacement = arguments.callee.prepareReplacement(replacement);
   doc(replacement);
     while (source.length > 0) {
       if (match = source.match(pattern)) {
         result += source.slice(0, match.index);
         result += String.interpret(replacement(match));
     // pass match (object) to replacement(function), 
     // return value replace match[0]...
     // origin Template.evaluate function recursive invoke String.gsub function
         source  = source.slice(match.index + match[0].length);
       } else {
         result += source, source = '';
       }
     }
     return result;
   },

   sub: function(pattern, replacement, count) {
     replacement = this.gsub.prepareReplacement(replacement);
     count = count === undefined ? 1 : count;

     return this.gsub(pattern, function(match) {
    //alert(match.index);
    //alert(match[0]);
       if (--count < 0) return match[0];
       return replacement(match);
     });
   }
 });
 
 String.prototype.gsub.prepareReplacement = function(replacement) {
   if (typeof replacement == 'function') return replacement;
   var template = new Template(replacement);
   return function(match) { return template.evaluate(match) };
 }

 var Template = Class.create();
 Template.prototype = {
   initialize: function(template, pattern) {
   alert(template.toString());
     this.template = template.toString();
   },

   evaluate: function(match_object) {
     return '<font color="red">' + this.template + '</font>';
   }
 }
 
 var str = 'ThereAreTest1AndTest2AndTest3.';
 var txt = str.gsub(/test/i, 'Text');
 doc(txt);
 
 var txt2 = str.sub(/test/i, 'Text', 2);
 doc(txt2);
</script>