Javascript Date format(format,value)

Date.prototype.format = function (format,value) {
 /*//from   w  w  w  .  j  a  v  a 2s  . c o m
  * eg:format="yyyy-MM-dd hh:mm:ss";
  */
 if (!format) {
  format = "yyyy-MM-dd hh:mm:ss";
 }
 if(value==''||value==null){
  return '';
 }
 var date = new Date(value);
 var o = {
  "M+" : date.getMonth() + 1, // month
  "d+" : date.getDate(), // day
  "h+" : date.getHours(), // hour
  "m+" : date.getMinutes(), // minute
  "s+" : date.getSeconds(), // second
  "q+" : Math.floor((date.getMonth() + 3) / 3), // quarter
  "S" : date.getMilliseconds()
  // millisecond
 };
 if (/(y+)/.test(format)) {
  format = format.replace(RegExp.$1, date.getFullYear());
 }
 
 for (var k in o) {
  if (new RegExp("(" + k + ")").test(format)) {
   format = format.replace(RegExp.$1, RegExp.$1.length == 1 ? o[k] : ("00" + o[k]).substr(("" + o[k]).length));
  }
 }
 return format;
};