Why not working?

Question

https://code.sololearn.com/W9O2h1GvXw09/?ref=app

Answer 1

I do not know why you would write:

if(el1)

https://code.sololearn.com/W9C95bwVKaxr/?ref=app

but here is the fixed code. I removed the if statement from the event Listeners section and made them get added only after Dom is loaded. ;)

Answer 2

window.onload = function()
{
// add event listener for the 3 elements here
}

At the moment the code refers to elements before the DOM is fully setup, the elements you refer to, are not yet prepared to be used.

Answer 3

Thanks Ćheyat and Ipang