https://denobiawards.com/js/save_gclid_cookie.js

1function setCookie(name, value, days) {
2    var date = new Date();
3    date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
4    var expires = "; expires=" + date.toGMTString();
5    document.cookie = name + "=" + value + expires + ";path=/";
6}
7
8function getParam(p) {
9    var match = RegExp('[?&]' + p + '=([^&]*)').exec(window.location.search);
10    return match && decodeURIComponent(match[1].replace(/\+/g, ' '));
11}
12var gclid = getParam('gclid');
13if (gclid) {
14    var gclsrc = getParam('gclsrc');
15    if (!gclsrc || gclsrc.indexOf('aw') !== -1) {
16        setCookie('gclid', gclid, 90);
17    }
18}