setCookie.js

// Store the name/value pair as a cookie, encoding the value with
// encodeURIComponent() in order to escape semicolons, commas, and spaces.
// If daysToLive is a number, set the max-age attribute so that the cookie
// expires after the specified number of days. Pass 0 to delete a cookie.
function setCookie(name, value, daysToLive=null) {
    let cookie = `${name}=${encodeURIComponent(value)}`;
    if (daysToLive !== null) {
        cookie += `; max-age=${daysToLive*60*60*24}`;
    }
    document.cookie = cookie;
}