jQuery验证码发送时间秒递减（刷新存储cookie）

<input id="sendEmail" type="button" name="sendEmail" onclick="show()" value="发送" style="cursor:pointer; width:218px;margin-left:3px;text-indent:0;text-align:center;margin-top:10px;"/>

function writeCookie(name, value, timeNum) {//把当前发送的时间写入cookie
var expire = "";
if (timeNum != null) {
expire = new Date((new Date()).getTime() + timeNum);//设置有效时间段（当前时间+设置的有效时间长度）
expire = "; expires=" + expire.toGMTString();//这里分号是为与前面的拼接需要"name=xxx;expires=yyy"
}
document.cookie = name + "=" + escape(value) + expire + ";path=/";
}
function readCookie(name) {//读取cookie中名称等于name的值
var cookieValue = "";
var search = name + "=";
if (document.cookie.length > 0) {
offset = document.cookie.indexOf(search);
if (offset != -1) {
offset += search.length;
end = document.cookie.indexOf(";", offset);
if (end == -1) end = document.cookie.length;
cookieValue = (document.cookie.substring(offset, end))
}
}
return cookieValue;
}

var tipId;
function show() {
writeCookie("daTime", (new Date()).getTime(), 60000)
tipId = window.setInterval("start()", 1000);
}
$(function () {
var tt = parseInt(((new Date()).getTime() - readCookie("daTime")) / 1000);
if (tt < 60) {
tipId = window.setInterval("start()", 1000);
var vv = "(" + parseInt(60 - tt) + ")秒后重新发送";
$("#sendEmail").attr("disabled", "disabled");
$("#sendEmail").attr("value", vv);
}
})
function start() {
var tt = parseInt(((new Date()).getTime() - readCookie("daTime")) / 1000);
if (tt < 60) {
var vv = "(" + parseInt(60 - tt) + ")秒后重新发送";
$("#sendEmail").attr("disabled", "disabled");
$("#sendEmail").attr("value", vv);

} else {
$("#sendEmail").removeAttr("disabled");
$("#sendEmail").attr("value", "发送");
window.clearInterval(tipId);
}
}