What wrong?

Question

https://code.sololearn.com/WWuX8uw5MYrf/?ref=app

Answer 1

The JavaScript error is from how you tried to access the document to link your click event handler before the document's content fully loaded.

Here is a fixed version of your JavaScript:

document.addEventListener('DOMContentLoaded', function() {
var left = document.getElementById('left');

left.onclick = function (){
alert ("test")
}
});

Answer 2

Ferenando my answer wasn't best as I didn't provide an explanation unlike Josh Greig

Answer 3

I think it's about lef. Onclick, if you want to make it simple, better delete that before the function, put a name to the function and use it as an onclick attribute within the tag and function name., it's easier like this, or instead you can use the getElement

Answer 4

Or try putting code inside following function

window.onload=function(){

}