Defining the onChange type independently #290

When using Next(typescript), I found that I couldn't use the onChange method's type when I wanted to use it.

When I examined the codes, I saw that the type of the onChange method is defined in the onChange method.

I would like to make a small update to the project and open a Pull request. Can I get a pull request?
(this is my first issue, if I'm doing something wrong, I'm sorry)