js 禁用和倒计时

//js代码

var n = 5;
var intervalID;
function setEnable(falg) {
    n--;
    if (n > 0) {
        falg.disabled = true;
        falg.value = "重新获取（" + n + "）";
    } else {
        $("hid_Random").val("");
        clearInterval(intervalID);
        falg.disabled = false;
        falg.value = "重新获取验证码";
    }
}

intervalID = window.setInterval(function() { setEnable(falg); }, 1000);

//html代码

<tr>
                    <td align="right" height="45">
                        验证码：
                    </td>
                    <td width="35%">
                        <input type="text" id="txtAlipay" runat="server" /><br />
                        <input type="button" value="获取验证码" onclick="GetRandomCode(1,this)" />
                    </td>
                    <td width="16%">
                        <span id="sp_Alipay" style="color: #ff6600;">(必填)</span>
                    </td>
                </tr>