Why can't html input functions be in JavaScript

Question

since JavaScript is embedded in HTML
why can't their functions be used interchangeably

Answer 1

Not sure I understand you question, can you provide an example please.

JavaScript can either be embeded in your HTML or in a separate .js file and just reference that file within your HTML. You write function in JavaScript to interact with your HTML (eg modify, add, remove elements). HTML can only call your JavaScript functions.