cookie的存取删

存：
document.cookie = "name=Kevin;expires="+new Date().getDate()+7; //有效期7天
取：
function GetCookie(sName)
{
var aCookie = document.cookie.split("; ");
for (var i=0; i < aCookie.length; i++)
{
var aCrumb = aCookie[i].split("=");
if (sName == aCrumb[0])
return unescape(aCrumb[1]);
}
return null;
}
GetCookie('name')      //Kevin

//设置cookie
function setCookie(cname, cvalue, exdays) {
    var d = new Date();
    d.setTime(d.getTime() + (exdays*24*60*60*1000));
    var expires = "expires="+d.toUTCString();
    document.cookie = cname + "=" + cvalue + "; " + expires;
}
//获取cookie
function getCookie(cname) {
    var name = cname + "=";
    var ca = document.cookie.split(';');
    for(var i=0; i<ca.length; i++) {
        var c = ca[i];
        while (c.charAt(0)==' ') c = c.substring(1);
        if (c.indexOf(name) != -1) return c.substring(name.length, c.length);
    }
    return "";
}
//清除cookie
function clearCookie(name) {
    setCookie(name, "", -1);
}
function checkCookie() {
    var user = getCookie("username");
    if (user != "") {
        alert("Welcome again " + user);
    } else {
        user = prompt("Please enter your name:", "");
        if (user != "" && user != null) {
            setCookie("username", user, 365);
        }
    }
}
checkCookie();