javascript money currency format with commas.js

String.prototype.addMoneyCommas = function(){
    return  $.map(
              $.grep(
                // the input str, reversed, broken into sets of three
                this.split('').reverse().join('').split(/(...)/),
                // with the oddly-blank entries removed
                function(str){if(0 != str.length) return true}
              ),
              function(str){
              // with the individual pieces then re-reversed
              return str.split('').reverse().join('')
            })
            // and then _those_ pieces re-reversed
            .reverse()
            // joined by commas
            .join(",")
  }