How to properly write the function for a button

Question

Please look at the JavaScript for my attached code here.

My question is, how is it best to have the function for the submit button on my app? Should I have the function only do the final equation when submit is clicked, and all of the other stuff is called beforehand? Or should it be how I currently have it?

My concern is that it won’t pull the info for getElementById() if it is not part of the submit button’s function. And also, what is considered proper for a calculator like this? Any input is appreciated!
https://code.sololearn.com/Wff2HPhJ1CS8/?ref=app

Answer 1

It is good why to do it properly write the function for a button . It is in proper way

Answer 2

Thanks bro

Answer 3

Do u have any idea about mobile programming