document.getElementByld("canvas1") means

Answer 1

It is a JavaScript method that finds the bit of code that has that ID and returns it as an object.

eg this will hide a div:

HTML: <div id = "getMe"> </div>

JAVASCRIPT: document.getElementById("getMe").style.hidden()

See more here: https://developer.mozilla.org/en-US/docs/Web/API/Document/getElementById

Answer 2

ok
And
Thank you for help