What's wrong with this?

Question

https://code.sololearn.com/Wk6k6fppDYHB/?ref=app

Answer 1

window.onload = function(){

//Your canvas code

}

Answer 2

Window onload function is needed because html is loaded before js
https://code.sololearn.com/WIkKiK75lyBW/?ref=app

Answer 3

Thank you all