Yes, you can. Go to Settings–Advanced– Form tab and tick the option Add a JS script to your form. Paste the script URL in the text box that shows up. UseĀ a reliable service to host your script files . This feature is available starting with the Platinum plan. Here is the 123FormBuilder features list.
If you need to track the numbers of users who submitted the form, simply add a script on the Thank-you Page.
Here is a list of the most frequently asked questions. For more FAQs, please browse through the FAQs page.