The React Fact That Will Change Your Mindset

THE FACT: ReactDOM.render is not destructive
If you repeatedly call ReactDOM.render on a component, passing in different props each time, then React doesn’t tear down that component and start from scratch. React updates the component’s props while maintaining its internal state. Before showing how this fact will change your mindset, let’s demonstrate its veracity with the aid of an example.
The example shows a Timer component that increments every second. The colour of the number displayed alternates between red and blue every other second. The Timer stores the seconds count in state and the display colour in props. To toggle the colour, we run a setTimeout every two seconds that calls ReactDOM.render passing the new colour prop to the Timer. You can see that ReactDOM.render is not destructive because the count, held in state, doesn’t reset when we change the colour:

You Don’t Need the React Router
Let’s modify the Timer example so that,


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