js使用cookie

//创建cookie
function addCookie(){
    var Days = 30;
    var exp = new Date();
    exp.setTime(exp.getTime() + Days*24*60*60*1000);
    document.cookie = "lastUserName" + "="+ escape (un) + ";expires=" + exp.toGMTString();
}
//读取cookie
function getCookie(name) {
    var arr,reg=new RegExp("(^| )"+name+"=([^;]*)(;|$)");
    if(arr=document.cookie.match(reg))
        return unescape(arr[2]);
    else
        return null;
}
//删除cookies
function delCookie(name) {
    var exp = new Date();
    exp.setTime(exp.getTime() - 1);
    var cval=getCookie(name);
    if(cval!=null){
        document.cookie= name +"="+cval+";expires="+exp.toGMTString();
    }else{
        document.getElementById("j_username").value="请输入用户名";
    }
}