js如何使用cookies

document.cookie = "username=John Doe; expires=Thu, 18 Dec 2023 12:00:00 UTC; path=/";

console.log(document.cookie);

document.cookie = "username=Jane Doe; expires=Thu, 18 Dec 2023 12:00:00 UTC; path=/";

document.cookie = "username=; expires=Thu, 01 Jan 1970 00:00:00 UTC; path=/;";

// 设置 Cookie
function setCookie(name, value, days) {
    var expires = "";
    if (days) {
        var date = new Date();
        date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
        expires = "; expires=" + date.toUTCString();
    }
    document.cookie = name + "=" + (value || "") + expires + "; path=/";
}

// 读取 Cookie
function getCookie(name) {
    var nameEQ = name + "=";
    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, c.length);
        if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length, c.length);
    }
    return null;
}

// 删除 Cookie
function eraseCookie(name) {
    document.cookie = name + '=; Max-Age=-99999999;';
}

// 使用示例
setCookie('user_preference', 'dark_mode', 7); // 设置一个7天后过期的 Cookie
console.log(getCookie('user_preference')); // 输出: dark_mode
eraseCookie('user_preference'); // 删除该 Cookie