wait_for_segment_set_hidden_inputs.js

const setHiddenInputValues = function(form, params) {
  const inputs = form.elements;
  inputsArr = Array.apply(null, inputs);
  
  hiddenInputs = inputsArr.filter(function(i) {
    return i.type === 'hidden';
  });

  // set value of inputs to the params passed in
  hiddenInputs.forEach(function(i) {
    key = i.name;
    val = params[key];
    if (val) {
      i.value = val;
    }
  });
};


analytics.ready(function() {
  console.log("SEGMENT READY")
  const params = {
    path: window.location.pathname, 
    url: window.location.href,
    search: window.location.search,
    referrer: document.referrer,
    title: document.title,
    anonymousId: analytics.user().anonymousId(),
    sessionId: amplitude.getSessionId(),
    userId: analytics.user().id()
  };
  
  // Grab all forms on the page, loop through them, 
  // and set their hidden fields to the corresponding params.
  const $forms = document.getElementsByTagName("form");
  const formsArr = Array.apply(null, $forms);
  
  formsArr.forEach(function(f) {
    setHiddenInputValues(f, params)
  });
})