String.prototype.comma=function() { var l_text=this; var l_pattern=/^(-?\d+)(\d{3})($|\..*$)/; if(l_pattern.test(l_text)){ l_text=l_text.replace(l_pattern,function(str,p1,p2,p3) { return p1.comma() + ("," + p2 + p3); }); } return l_text; } 출처 : 스쿨 Tip & Tech .