Tracking an email signup form, where you don't know the user's identity until the form is submitted, and the form is actually submitted to a 3rd-party mailing list so you don't have control over what happens when it's submitted.

trackForm.js

// Grab the form using whichever DOM library you're using, or 
// even just with `querySelector`.
var $form = $('#my-form'); 

// Call `trackForm` with your form, and a callback function
// instead of a normal `properties` object. The function will
// receive the form element as it's first argument.
analytics.trackForm($form, "Email Signup", function (form) {
  
  // Find the email input and get it's value.
  var email = $(form).find('.email-address').val();
  
  // Send off the identify.
  analytics.identify(email);
});