<solved>Compatibility issues?(android)

Question

So I wrote this code and everything works just fine on my iPhone but when I testet it on android (I wanted to see how it looks on a different screen size) it showed me an error message.
The error:
"Uncaught TypeError: Cannot read properties of null (reading 'getContext')
Line: 4"
Can anybody explain what is happening and how I can fix this?

https://code.sololearn.com/W74ue81u1ssd/?ref=app

Answer 1

https://code.sololearn.com/W9eNFfSdrEOG/?ref=app

You should add before your code starts:
window.onload=function(){

And close the curly braces at the end.
}

Answer 2

Thank you that worked 👍