The code doesn't work

Question

Below there is my first "non-one-line code" :)
This is a calculator. Yes, it is far from perfect, but it works.
Made on PC, it works there, but the application shows errors. I hope for your help and advice on improving the code. Thanks!
https://code.sololearn.com/Wh2J6NIqg43e/?ref=app

Answer 1

Wrap your javascript into

window.onload = () => {
// Your code

}

Answer 2

You are welcome. Try to answer others questions.

Answer 3

Thank you Vivek. Now everything works!