Adding an event listener

Question

What is the problem with this js code i can't figure it out. I don't know how to ask it in a question.
https://code.sololearn.com/WpodOJewvFu5/?ref=app

Answer 1

since js is loaded and executed first (unless you invoke it not to or add script tag after body), it does not know what the document has.
wrap your DOM code inside a window.onload event so
window.onload = () => {
// your code
}

Answer 2

PUT your js code inside
window.onload=function()
{
}
here's a good reference
https://www.sololearn.com/post/7444/?ref=app

Answer 3

「ＨＡＰＰＹ ＴＯ ＨＥＬＰ」, Hima
thank you it worked!