Read (Get) Cookie Expiry date and time in jQuery

I use below code buts not returning the expiry date and time of cookie.

 function getCookie(cookieName) {
    var name = cookieName + "=";
    var decodedCookie = decodeURIComponent(document.cookie);
    var cookieArray = decodedCookie.split(';');
    for (var i = 0; i < cookieArray.length; i++) {
        var cookie = cookieArray[i];
        while (cookie.charAt(0) === ' ') {
            cookie = cookie.substring(1);
        }
        if (cookie.indexOf(name) === 0) {
            return cookie.substring(name.length, cookie.length);
        }
    }
    return "";
}

function getCookieExpiration(cookieValue) {
    var expirationIndex = cookieValue.indexOf(";expires=");
    if (expirationIndex === -1) {
        return null;
    }
    var expirationString = cookieValue.substring(expirationIndex + 9);
    return new Date(expirationString);
}

$(document).ready(function() {
    var cookieValue = getCookie("ServiceMate-CookieShow");
    var cookieExpiration = getCookieExpiration(cookieValue);
    if (cookieExpiration !== null) {
       alert("Cookie Expiry Date: " + cookieExpiration);
        // Perform further actions with the cookie expiry date
    }

    alert("Cookie Expiry Date: ");
});