Using ECMAScript Modules

Open developer tools and have a look at the network tab in both older and modern browsers for the scripts loaded and the script sizes.

native date input (if supported):

This should have the date value set to 2020-04-05 and only allow a minimum date of 2020-04-03 and maximum 2020-04-19. lang="de-DE", which should only effect the date input display if a de language is installed on the browser.