//JS操作cookies方法!
//设置cookies
function setCookie(cname, cvalue, exdays) {// days设置过期时间 单位:天 不传默认是 cookie 在浏览器关闭时删除
    var d = new Date();
    d.setTime(d.getTime() + (exdays * 24 * 60 * 60 * 1000));
    var expires = "expires="+d.toUTCString();
    delCookie
    document.cookie = cname + "=" + cvalue + ";" + expires + ";path=/";
}
//读取cookies
function getCookie(cname) {// 获取一个cookie
    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)  == 0) {
            return c.substring(name.length, c.length);
        }
    }
    return "";
}
//删除cookies
function delCookie(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);
        }
    }
}

//使用示例
/*setCookie("name","123");
alert(getCookie("name"));*/

参考：JavaScript Cookies

原生JS的cookie操作

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