js写一个倒计时效果

// 倒计时 this.timer = setInterval(function () { var time1 = new Date( res.data[0].uploadtime ).getTime(); var time2 = new Date().getTime(); var time30 = 30 * 60 * 1000; var diff = time2 - time1; if (diff <= time30) { var min = parseInt((time30 - diff) / 1000 / 60); var sec = parseInt( ((time30 - diff) / 1000) % 60 ); _this.countdown = min + " : " + sec; } else { _this.countdown = “已超时”; } }, 500);