Use of document.getElementById in JavaScript

Question

Can someone explain what the document.getElementById(\"demo\") line does in the example below?

I understand getElementById gets the id of demo but the id is

Answer 1

Here in your code demo is id where you want to display your result after click event has occur and just nothing.

You can take anything

<p id="demo">

or

<div id="demo"> 

It is just node in a document where you just want to display your result.