JS help needed. Can not read value of null

Question

I have created this small program that tells you if the entered value is an even number or not. I have noticed that there is an error that shows that it can not read a value of null. How can i fix it? The program works fine but i would still like to know how to fix the error and why it happend. Thx for the help.
https://code.sololearn.com/W5Bn2CWR2dbE/?ref=app

Answer 1

Quick solution : comment or remove your line 16.

Explanation :
You are trying to find the DOM before it exists. See following demo for details:
https://code.sololearn.com/WriFNOoR188j/?ref=app