Criar função de cookie com Vanilla JS

Crie cookies facilmente com vanilla javascript.

function createCookie(name, value, days) {
    if (days) {
        var date = new Date();
        date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
        var expires = "; expires=" + date.toGMTString();
    } else var expires = "";
    document.cookie = escape(name) + "=" + escape(value) + expires + "; path=/";
}