You said 'Cookies' Right? Here is a method from tutorialsrepublic.com
To set Cookies
function setCookie(name, value, daysToLive = undefined) {
    // Encode value in order to escape semicolons, commas, and whitespace
    var cookie = name + "=" + encodeURIComponent(value);
    
    if (typeof daysToLive === "number") {
        /* Sets the max-age attribute so that the cookie expires
        after the specified number of days */
        cookie += "; max-age=" + (daysToLive*24*60*60);
    }
        
    document.cookie = cookie;
}
To get Cookies
function getCookie(name) {
    // Split cookie string and get all individual name=value pairs in an array
    var cookieArr = document.cookie.split(";");
    
    // Loop through the array elements
    for(var i = 0; i < cookieArr.length; i++) {
        var cookiePair = cookieArr[i].split("=");
        
        /* Removing whitespace at the beginning of the cookie name
        and compare it with the given string */
        if(name == cookiePair[0].trim()) {
            // Decode the cookie value and return
            return decodeURIComponent(cookiePair[1]);
        }
    }
    
    // Return null if not found
    return null;
}
And to reassign cookies, just use the same one as set.
setCookie(Name, NewValue, Days)
Example:
Finally, to delete cookies you can use
setCookie(Name, '', 0)
For Localstorage, Go here