Shopify: get URL parameters when a customer visits my shop

A possible solution would be to read the url parameters from the Order-Webhook under the referring_site-Element. It usually looks like this:

"referring_site": "https://{shop}.myshopify.com/products/testprodukt-1"

But the problem is that the parameters disappear when the customer changes the page. So it is not shown on the referring_site-Element of the webhook.

So my plan looks like this:

Insert a Shopify-Scripttag:

'scripttags' => [
    [
        'src' => 'https://{domain}/scripttags/dummy.js',
        'event' => 'onload',
        'display_scope' => 'online_store'
    ]
]

dummy.js:

// some cookie functions
function setCookie(name,value,days) {
    var expires = "";
    if (days) {
        var date = new Date();
        date.setTime(date.getTime() + (days*24*60*60*1000));
        expires = "; expires=" + date.toUTCString();
    }
    document.cookie = name + "=" + (value || "")  + expires + "; path=/";
}
function getCookie(name) {
    var nameEQ = name + "=";
    var ca = document.cookie.split(';');
    for(var i=0;i < ca.length;i++) {
        var c = ca[i];
        while (c.charAt(0)==' ') c = c.substring(1,c.length);
        if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
    }
    return null;
}

//get params
const url_string = window.location.href;
const url_object = new URL(url_string);
const my_param = url_object.searchParams.get("my_param");

if (my_param != null) {
    
    //set cookie
    setCookie('my_param', my_param);

}else{

    //get cookie
    let my_param_cookie = getCookie('my_param');

    if (my_param_cookie) {

        //set params from cookie

        let url_all_params = '';
        const url_pathname = url_object.pathname;
        const url_params = url_object.search;
        const url_seperator = url_params == '' ? '?' : '&';
        const url_my_param = my_param == null ? 'my_param=' + my_param_cookie : my_param;

        url_all_params = url_pathname + url_params + url_seperator + url_my_param;

        if (history.pushState) {
            window.history.pushState({}, "", url_all_params);
        } else {
            document.location.href = url_all_params;
        }
    }
}

To the code above:

1. Find the parameter you are looking for
2. When you find it, save it in a cookie
3. If you haven't found it, see if the cookie exists
4. If the cookie exists, get the parameter you are looking for and add it to the URL
5. If the cookie doesn't exist, do nothing

This will make the referring_site look like this in the order webhook:

"referring_site": https://{shop}.myshopify.com/products/testprodukt-1/?myparam=1

Now you can do what you want with the parameter in the backend, I hope I could help or provide inspiration.