When will you use this?

You use this in every component you write from your first app to your tenth year on the job.

• Product pages, login forms, and todo lists all use components, props, and state.
• When a user types in a search box, React state holds the text and filters a list.

Real-world: Amazon seller SKU row

Amazon Seller Central lists thousands of SKUs. Parent InventoryTable passes sku, stock, and price as props to InventoryRow — the row never fetches; it only displays what it receives.

Production-style code

function InventoryRow({ sku, title, stock, price, onEdit }) {
  const lowStock = stock < 10;
  return (
    <tr className={lowStock ? 'row-warning' : ''}>
      <td>{sku}</td>
      <td>{title}</td>
      <td>{stock}</td>
      <td>₹{price.toLocaleString('en-IN')}</td>
      <td><button type="button" onClick={() => onEdit(sku)}>Edit</button></td>
    </tr>
  );
}

function InventoryTable({ items, onEditSku }) {
  return (
    <table>
      <tbody>
        {items.map(item => (
          <InventoryRow key={item.sku} {...item} onEdit={onEditSku} />
        ))}
      </tbody>
    </table>
  );
}

What happens in production: Props keep rows pure and testable — QA passes fake props to InventoryRow without mocking the whole inventory API.

Lesson example (start here)

Copy this smaller example first. Once it works, compare it with the real-world code above.

function ProductCard({ name, price }) {
  return (
    <div>
      <h2>{name}</h2>
      <p>₹{price}</p>
    </div>
  );
}

<ProductCard name="Keyboard" price={2499} />

Line-by-line walkthrough

How it works (big picture)

• The parent passes name and price.
• ProductCard cannot change props — if it needs to update data, use state in the parent and pass new props down.

Do this on your computer

1. Add a prop to a component and display it.
2. Pass a number with price={2499} not price="2499" unless you want a string.
3. Use default values: function Card({ title = "Untitled" }).
4. Read the real-world section and name which part of the app uses this topic.
5. Run the example locally and confirm the same behavior in the browser.
6. Change one value in the example (text, initial state, or URL) and predict what will happen before you save.

Experiments — try changing this

• Change text or labels in the example and save — watch the browser update.
• Break the code on purpose (remove a bracket), read the error message, then fix it.

Remember

Props = data from parent to child. Read-only in the child. Use destructuring in the parameter list.

Common questions