javascript日期与周转换笔记

1.查询某个日期是今年第几周：

1 var weekofyear =  (new Date(2017,3,13)-new Date("2017-01-01"))/(24*60*60*7*1000)|0+1;
2 
3 console.log('第'+weekofyear+'周' );

输出：第15周

2.周转具体日期：

var tDate = new Date();
var day = (function(){
    var tYear = 2017
    var tWeek = 15; //2017年第15周
    tDate = new Date(((tWeek+1)*7+(tYear-1970)*365)*24*60*60*1000);
    var day = tDate.getDay();
    return (day==0)?7:day;
})();

var monday =new Date(tDate.getTime() - (day)*24*60*60*1000);
console.log(monday.getFullYear()+'-'+(monday.getMonth()+1)+'-'+(monday.getDate()+1));

输出：2017-4-10