Convert the obtained timestamp to a countdown

getEndTime(endtime){
    
    
                                let timer = setInterval(() => {
    
    
                                        // 当前时间戳（ms）
                                        let nowTime = (new Date).getTime();
                                        // 倒计时(s)
                                        let resTime = Math.floor((parseInt(endtime) - nowTime/1000));
                                        if(resTime < 0){
    
    
                                                clearInterval(timer);
                                                return
                                        }
                                        // 转成时分秒
                                        let h = Math.floor(resTime / 3600);
                                        h = h < 10 ? '0' + h : h;
                                        let m = Math.floor((resTime % 3600) / 60);
                                        m = m < 10 ? '0' + m : m;
                                        let s = resTime % 60;
                                        s = s < 10 ? '0' + s : s;
                                        this.killTime.h = h;
                                        this.killTime.m = m;
                                        this.killTime.s = s;
                                },1000)
                        }