Issue

ReactDOM.render(
  <App />,
  document.getElementById('root')

So what should I understand when i see something like this at the end of the app? What does 'root' or 'demo' stand for?

Solution

It's the element that exists in the original HTML that all of the React contents go into. For example, if your HTML contains:

<body>
  <div>Maybe some other content here</div>
  <div id="root"></div>
</body>

React rendering into the #root means that everything App renders will be put into that element:

<div id="root"> 
  <!-- App populates this element -->
</div>

The element selected to be populated can be any element you want - it doesn't have to be root or demo in particular.

Answered By - CertainPerformance
Answer Checked By - - Mary Flores (ReactFix Volunteer)