//cookieを読込
function getCookie(key) {
    var i, index, arr;
    arr = document.cookie.split(";");
    for(i = 0; i < arr.length; i++) {
        index = arr[i].indexOf("=");
        //2番目は頭がスペースのとき
        if(arr[i].substring(0, index) == key ||
                arr[i].substring(0, index) == " " + key)
            return arr[i].substring(index + 1);
    }
    return "";
}

//cookieを保存
function setCookie(key, value) {
    document.cookie = key + "=" + value ;
}

//cookieを破棄
function clearCookie(key) {
    document.cookie = key + "=" + "xx; expires=Tue, 1-Jan-1980 00:00:00;";
}