倒计时

function timeCount() {
    var tar = new Date('2018/7/22 18:30:00').getTime();
    var now = new Date().getTime();
    var time = tar - now;
    if(time <= 0){
        clearInterval(timer2);
        time = 0;
    }
    var h = Math.floor(time/3600000);
    time = time - h*3600000;
    var m = Math.floor(time/60000);
    time = time - m*60000;
    var s = Math.floor(time/1000);
    var str = `距离下课还有${h<10?'0'+h:h}小时${m<10?'0'+m:m}分钟${s<10?'0'+s:s}秒`;
    var oDiv = document.getElementById('div1');
    oDiv.innerText = str;
}

var timer2 = setInterval(function () {
    timeCount();
},1000);