SOURCE

$(function(){
	    /*当前时间*/
	    var t = null;
	    function clock(){
	        var _date = new Date();
		    var _y = _date.getFullYear();
		    var _m = _date.getMonth()+1;
		    var _d = _date.getDate();
		    var _h = checkTime(_date.getHours());
		    var _ms = checkTime(_date.getMinutes());
		    var _s = checkTime(_date.getSeconds());
		    document.getElementById('date').innerHTML ='当前时间 : ' + _y + '-' + _m + "-" + _d + '&nbsp' + _h +':' + _ms +':' + _s;
		    t = setTimeout(clock,1000);
	    }
	    	clock(); 
    	})
    	function countdown(et){
    		var _start = new Date();
    		var _end = new Date(et);
    		var _countdown = ((_end.getTime()-_start.getTime())/1000);
    		var _d = parseInt(_countdown/(60*60*24));
    		var _h = parseInt(_countdown/(60*60)%24);
    		var _m = parseInt(_countdown/60%60);
    		var _s = parseInt(_countdown%60);
    		document.getElementById('countdown').innerHTML = '距离活动开始还有' + checkTime(_d) + '天' +checkTime(_h) +'小时'+checkTime(_m)+'分'+checkTime(_s) + '秒';
    		ts = setTimeout(function(){countdown('2020/7/18 24:00:00')},1000);
    	}
    	function checkTime(i){
	    	return i<10 ? i= '0'+i : i;	
	    }
   	    window.onload = function(){
   		 	var ts = null;
    		countdown('2020/7/18 24:00:00');
    	}

<div id="date"></div>
<div id="countdown"></div>