js倒计时

<input id="deviceDiagnose" type="button" onclick="deviceDiagnose(this)"  value="重新检测">

var wait=300;  
function timer(obj) {
        if (wait == 0) { 
        obj.removeAttribute("disabled");    
        obj.value="重新检测"; 
        wait = 5; 
        } else { 
        obj.setAttribute("disabled", true); 
        obj.value="重新检测(" + parseInt(wait/60) + "'"+(wait%60)+")"; 
        wait--; 
        setTimeout(function() { 
            timer(obj) 
        },1000) 
        } 
    }