JavaScript日期格式化

Date.prototype.format = function(format) { 
  var o = { 
    "M+" : this.getMonth()+1, //month 
    "d+" : this.getDate(),    //day 
    "h+" : this.getHours(),   //hour 
    "m+" : this.getMinutes(), //minute 
    "s+" : this.getSeconds(), //second 
    "q+" : Math.floor((this.getMonth()+3)/3),  //quarter 
    "S" : this.getMilliseconds() //millisecond 
  } 
  if(/(y+)/.test(format)) format=format.replace(RegExp.$1, 
    (this.getFullYear()+"").substr(4 - RegExp.$1.length)); 
  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; 
 } 


 var now=new Date().format("yyyy-MM-dd");