cookie的使用

//cookie部分
//设置cookie
//注意cname传入字符串类型，如：setCookie('first');
function setCookie(cname,cvalue,exdays){
    var d = new Date();
    d.setTime(d.getTime()+(exdays*24*60*60*1000));
    var expires = "expires="+d.toGMTString();
    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].trim();
        if (c.indexOf(name)==0) return c.substring(name.length,c.length);
    }
    return "";
}
//检查cookie
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,30);
        }
    }
}
//删除单个cookie
function clearCookie(name) {
    setCookie(name, "", -1);
}
//删除所有cookie
function clearAllCookie(){
    var keys=document.cookie.match(/[^ =;]+(?=\=)/g);
    if (keys) {
        for (var i =  keys.length; i--;)
            document.cookie=keys[i]+'=0;expires=' + new Date( 0).toUTCString()
    }
}