发送手机验证码倒计时

(js代码)

<script type="text/javascript">
        var i = 60;
        function page_cg() {
            document.getElementById("getCheckNum").value ="免费获取验证码("+i+")";
            if (i > 0) {
                i--;
            }
            else {
                document.getElementById("getCheckNum").disabled = 0;  //可用
            }
            window.setTimeout(function () { page_cg() }, 1000);
        }
    </script>

(后台代码)

this.getCheckNum.Enabled=false;
//如果短信发送成功，获取js代码
/*
 * */
Page.RegisterStartupScript("err","<script language>window.onload = page_cg;</script>");