I am creating an ajax request to subscribe to newsletter. The platform is Shopify so its a limited resource available for me to validate if the form is successful or not.

I would like to add a error message if email is already subscribed.

I created an ajax function that post data to Shopify URL /contact#contact_form.

According to Shopify it does not return any error or message when email is already registered. One thing we can do is just checking if the posted URL has ?contact_posted=true then it means the form is successful. Otherwise I am assuming email is already registered.

On ajax success function how do I check if the submitted URL has this query string parameter ?contact_posted=true. Fyi the form action is redirected from /contact#contact_form to ?contact_posted=true on success.

Any help would be appreciated.