Idea: Improve pat-formunloadalert

Instead of marking a form as dirty as soon as events on input types are triggered we could instead on beforeunload compare the original input.value to input.defaultValue, available in browsers since 2015.

https://developer.mozilla.org/en-US/docs/Web/API/HTMLInputElement/defaultValue

I have a situation where opening the properties editing form in a mosaic layout edit view triggers a false form unload alert. If we would compare the original values to the current values, this would not happen.

const form = document.querySelector("form.pat-formunloadalert");

[...form.elements]
  .map(el => {
    let current, initial;

    if (el.type === "checkbox" || el.type === "radio") {
      current = el.checked;
      initial = el.defaultChecked;
    } else if (el.tagName === "SELECT") {
      current = [...el.options].map(o => o.selected);
      initial = [...el.options].map(o => o.defaultSelected);
    } else {
      current = el.value;
      initial = el.defaultValue;
    }

    return {
      name: el.name,
      id: el.id,
      type: el.type,
      current,
      initial,
      changed: JSON.stringify(current) !== JSON.stringify(initial)
    };
  })
  .filter(x => x.changed);

Start at the pat-formunloadalert implementation and inspect its beforeunload handling. Compare each form control's current state with its default state as described in the issue, then verify that unchanged forms do not trigger an alert while changed forms still do.