fix my client side storage Javascript script

Hi I need someone to fix my Javascript code and make it cross browser compatible with client side storage. Basically I have a form on my wordpress site and I want to capture a tag from the landing page URL and save that tag. Then I want to capture the users first name, last name, and email when they enter it on the checkout page (woocommerce). As soon as they enter their email and the email form loses focus (blur event in Javascript) I want to capture the email first and last name and then use that information to submit an invisible Autoresponder form and add the user to a list. (think of abandoned cart plugins for woocommerce. It's basically like that with the above logistics using Javascript on the WordPress site.) the tag that I capture from the URL will be used to decide which list to add the user to. This plugin will do all the submitting on the woocommerce checkout page and then again on the woocommerce order received page. It will need to be able to grab the tag from the URL on any page of the site that has the tag when the user lands on it. Now the rest of the details are that once a user has grabbed a tag and submitted their credentials to the list, they will not be added again so the forms need to only submit a user one time to each list. So that is what I tried to accomplish by myself using Javascript and I have it working for desktop browsers using cookies to store the information but I can't get it working for mobile phones which is the most important part I need. I tried using localStorage but that didn't work on safari or iPhone so I tried using localForage and got farther but still had issues so lastly I tried cookies like mentioned above. It seems no matter what I try I can't get it working for all rowers and iPhone and android phone. I am not a pro coder so I am stumped at this piont and looking for someone who knows how to fix the issue and make the script work on all browsers so it works every time. Please let me know if you can do this and what your experience is. If it's easier to create a wordpress plugin or do it using PHP that's fine with me too I just want it to work properly.