No output to my code

Question

var elem = document.getElementById("demo");
elem.innerHTML ="Hello World";

Is there anything wrong with the code 'cause its not giving any output when i run it in browser.
This is just to clarify my previous question.

Answer 1

Can you add complete code..?

Answer 2

https://www.sololearn.com/Discuss/2405741/?ref=app

Answer 3

I think you need to complete next chapter in same lesson - "Working with dom". There is complete example, run it by "try it yourself" and observe.
It is used to change div elements but you should have div elements first. The example give clear idea. Go on...