Countdown to get verification code

<input name='code' type='submit' id='get_code' value='get verification code'>

$('#get_code').click(function(){
var num = 5;  
var i = setInterval(function() {  
    num -- ;  
    $("#get_code").attr("disabled", true); 
    $("#get_code").val(num+"秒");
    if (num==0){  
        clearInterval(i);
        $( "#get_code").val("Re-get" );
        $("#get_code").attr("disabled", false);  
    }  
}, 1000);

});