简单倒计时

//方法

function countdown(time){    var resource_time = parseInt(time);    var timer = setInterval(function(){        if(resource_time>0){            var days = Math.floor(resource_time/86400),                hours = Math.floor((resource_time%86400)/3600),                minutes = Math.floor(((resource_time%86400)%3600)/60),                seconds = Math.floor(((resource_time%86400)%3600)%60);            var time;            if(days>0){                time =days +"<span>天</span>" + hours +" : "+minutes+" : "+seconds;            }else{                time =hours +" : "+minutes+" : "+seconds;            }            $('.ac-timer').html(time);            --resource_time;        }else{            $('.ac-timer').html("0 : 0 : 0");            clearInterval( timer );        }    }, 1000);}