js实现验证码获取倒计时60秒

html:

<input  id="btn" type="button" style="float:left" value="免费获取验证码"/>

js:

<script type="text/javascript">
    var wait=60;
    function time(o) {
        if (wait == 0) {
            o.removeAttribute("disabled");
            o.value="免费获取验证码";
            wait = 60;
        } else {
            o.setAttribute("disabled", true);
            o.value="重新发送(" + wait + ")";
            wait--;
            setTimeout(function() {
                    time(o)
            }, 1000)
        }
    }
    document.getElementById("btn").onclick=function(){time(this);}
</script>