Can fields in <form> act dinamically?

Question

For example we calculate field one and two and show the result is in field three.

Answer 1

Use onkeyup attribute in form tag

https://code.sololearn.com/Wm2somj6fDNi/?ref=app

Answer 2

Yes, it can.

Answer 3

You can add it directly on html, since it's simple calculation

Answer 4

Yup you can, you have to learn javascript for that. And especially selectors.