var d = new Date();
var year = d.getFullYear();//当前年份
var month = d.getMonth() + 1; //当前月份
var day = new Date(year, month, 0); //当前日
var lastdate = year + '-' + month + '-' + day.getDate();    //获取月份的最后一天
lastdate = new Date(lastdate).format('yyyy-MM-dd');

 

Date.prototype.format = function(format) { 
    /* 
    * 使用例子:format="yyyy-MM-dd hh:mm:ss"; 
    */ 
    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; 
}