I am getting error in my web calculator. Please help

Question

I am getting "cannot read properties of null" error on my js
https://code.sololearn.com/WJwjengB4XgI/?ref=app
https://code.sololearn.com/WJwjengB4XgI/?ref=app

Answer 1

You cant select element before it is loaded, so you get null, wrap your code inside window.onload like I did in this code, check JS tab
https://code.sololearn.com/WPHmkG0Q5hCD/?ref=app