Changing html with JavaScript

Question

Where's the problem in this code https://code.sololearn.com/W7kWuF8ae4vI/?ref=app?

Answer 1

There are two problems with your code!

#1: you used document.getElementsById() instead of document.getElementById()
...the Element should not contain "s" since "Id" is singular not plural like "ClassName or TagName"

#2 you must either add your function(s) inside the html element <script> tag or wrap all your function(s) up in "window.onload" since you wanted to get something out of the DOM or WINDOW

...heres a modified version of your code.
https://code.sololearn.com/WsuM3dYda9TJ/?ref=app

Answer 2

So, "window.onload" is obligate, when we're working with DOM?

Answer 3

You need to put the part of your code where you collect the user input anf call the function red blue or green in a function.
You then need to set that function equal to window.onload

The cide fails because the FOM has not finished loading so document.getElementById("main") returns null.