What is the reason for writing onChange to the input?

Question

React

Why hang on the onChange input to change if the user already changes its value ?
There is a more detailed answer than in the documentation, where it says: is it necessary?

Answer 1

How does the state know that the value of the input has changed? The fact that the user has changed the text in the input is only visible to the user. Even in native JS, you attach an event handler to the input to track value changes.

Answer 2

https://ru.react.js.org/docs/forms.html