js日期显示，倒计时，时间比较

 日期显示：

var date = new Date();   //获取系统当前时间

time(date);   //输出xxxx年xx月xx时xx分 星期x

function time(d){
  var year = d.getFullYear();
  var month = d.getMonth()+1;
  var date = d.getDate();
  var hours = d.getHours();
  var minutes = d.getMinutes();
  var seconds = d.getSeconds();
  var day = d.getDay();
  var now = year +'年'+ month +'月'+ date +'日'+' '+ hours +'时'+minutes+'分'+''+'星期'+ day;
  console.log(now);
}

var tamp = date.getTime()；//转换成时间戳

倒计时

Math.floor向下取整。

function countTime() {  
    var date = new Date();        //获取当前时间  
    var now = date.getTime();     //转换时间戳 
    var str="2019/5/20 00:00:00"; //结束时间 
    var endDate = new Date(str); 
    var end = endDate.getTime();  
     
    var time = end-now;       //时间差   
    var d,h,m,s;  
    if (time>=0) {  
        d = Math.floor(leftTime/1000/60/60/24);  
        h = Math.floor(leftTime/1000/60/60%24);  
        m = Math.floor(leftTime/1000/60%60);  
        s = Math.floor(leftTime/1000%60);                     
    } 
    setTimeout(countTime,1000);  
}

  //2018-10-09 换成 2018/10/09 再转时间戳
  function day(d){
     var dateTime = d.replace(/\-/g,'/');
     var time = new Date(dateTime).getTime();
     return time;
  }