Project files and app entry

What this means

A React app has an entry file where React connects your component tree to a real HTML element. In many starter projects, the root component is called App, and React renders it into an element with an id like root.

In beginner terms, this topic answers one practical question: "What should I write, and why does React care about it?" Do not try to memorize the syntax first. First understand the idea, then connect the syntax to that idea.

Why it matters

Knowing the entry point helps you debug. If nothing appears, you can check whether the root element exists and whether your App component is being rendered.

When you build real React screens, this idea helps you decide where data should live, what the user should see, and what should happen after an interaction. That is why this lesson is part of the main path instead of being an optional detail.

Step by step

1. Notice the UI problem this topic solves. 2. Look at the smallest possible example. 3. Change one value and predict what should appear. 4. Run the example and compare the result with your prediction. 5. Use the practice task before moving on.

Small example

ReactDOM.createRoot(document.getElementById("root")).render(<App />);

Common mistake

Do not rename the root element id in HTML without also updating the JavaScript that looks for it.

Practice task

Find the line in a starter app that renders <App />, then explain what HTML element it connects to.

Remember this

React starts by mounting a component tree into one HTML root.