attribution.js

https://jennamolby.com/how-to-use-cookies-to-capture-url-parameters/

let YOUR_DOMAIN = "YOUR_DOMAIN.TLD" // ex: scrapingbee.com

function getParameterByName(name) {
	name = name.replace(/[\[]/, "\\[").replace(/[\]]/, "\\]");
	var regex = new RegExp("[\\?&]" + name + "=([^&#]*)"),
		results = regex.exec(location.search);
	return results === null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}
// Give the URL parameters variable names
var utm_source = getParameterByName('utm_source');
var utm_medium = getParameterByName('utm_medium');
var utm_campaign = getParameterByName('utm_campaign');
var utm_term = getParameterByName('utm_term');
var now = new Date();
now.setMonth( now.getMonth() + 1 );

function getCookie(cname) {
                var name = cname + "=";
                var decodedCookie = decodeURIComponent(document.cookie);
                var ca = decodedCookie.split(';');
                for(var i = 0; i <ca.length; i++) {
                    var c = ca[i];
                    while (c.charAt(0) == ' ') {
                        c = c.substring(1);
                    }
                    if (c.indexOf(name) == 0) {
                        return c.substring(name.length, c.length);
                    }
                }
                return "";
            }
 
// Set the cookies
if(utm_source != "" && getCookie("utm_source") == "") {
	document.cookie = `utm_source=${utm_source}; domain=${YOUR_DOMAIN}; expires="${now.toUTCString()}"`
}
if(utm_medium != "" && getCookie("utm_medium") == "") {
	document.cookie = `utm_medium=${utm_medium}; domain=${YOUR_DOMAIN}; expires="${now.toUTCString()}"`
}
if(utm_campaign != "" && getCookie("utm_campaign") == "") {
	document.cookie = `utm_campaign=${utm_campaign}; domain=${YOUR_DOMAIN}; expires="${now.toUTCString()}"`
}
if(utm_term != "" && getCookie("utm_term") == "") {
	document.cookie = `utm_term=${utm_term}; domain=${YOUR_DOMAIN}; expires="${now.toUTCString()}"`
}
if(document.referrer != "" && getCookie("referrer") ==  "") {
   	document.cookie = `referrer=${document.referrer}; domain=${YOUR_DOMAIN}; expires="${now.toUTCString()}"`
}

// Set the cookies
var utm_journey = getCookie("utm_journey");
var current_relative_path = location.href.replace(location.origin,'');
if (utm_journey != "") {
	old_journey = atob(utm_journey)
	new_journey = `${old_journey} - ${current_relative_path}`
	document.cookie = `utm_journey=${btoa(new_journey)}; domain=${YOUR_DOMAIN}; path=/;`
} else {
	document.cookie = `utm_journey=${btoa(current_relative_path)}; domain=${YOUR_DOMAIN}; expires="${now.toUTCString()}; path=/;`
}

For some reason, the Expires value was always set to Session instead of one month from now. I tried different things but it didn't work, so ended up using something that I already use, see below.

• Function to set cookie
• Added SameSite attribute with fallback for older browsers (see code comments for links with info)

Feel free to update the Gist with this!

function getParameterByName(name) {
	name = name.replace(/[\[]/, "\\[").replace(/[\]]/, "\\]");
	var regex = new RegExp("[\\?&]" + name + "=([^&#]*)");
	var results = regex.exec(location.search);
	return results === null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}

// Give the URL parameters variable names
var utm_source = getParameterByName('utm_source');
var utm_medium = getParameterByName('utm_medium');
var utm_campaign = getParameterByName('utm_campaign');

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

function setCookie(cname, cvalue) {
    const d = new Date();
    d.setTime(d.getTime() + (30 * 24 * 60 * 60 * 1000)); // 30 = number of days
    const expires = `expires=${d.toUTCString()}`;
    // Using the new SameSite attribute: https://web.dev/samesite-cookie-recipes/
    document.cookie = `${cname}=${cvalue};${expires};path=/;SameSite=Strict`;
    // Fallback for legacy browsers: https://web.dev/samesite-cookie-recipes/
    document.cookie = `${cname}=${cvalue};${expires};path=/;Secure`;
}
 
// Set the cookies
if(utm_source != "" && getCookie("utm_source") == "") {
    setCookie('utm_source', utm_source);
}
if(utm_medium != "" && getCookie("utm_medium") == "") {
	setCookie('utm_medium', utm_medium);
}
if(utm_campaign != "" && getCookie("utm_campaign") == "") {
	setCookie('utm_campaign', utm_campaign);
}
if(document.referrer != "" && getCookie("referrer") ==  "") {
    setCookie('referrer', document.referrer);
}

This is nice! Thank you very much.