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React basics: Looping a list

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How to loop over an array in React

13 Oct, 2021 Β· 2 min read

In today's article for React basics, we'll enhance our first ever React components with a list.

Yesterday we made some static book components like so:

<Book title='Laravel collections' />
<Book title='Ruby for beginners' />
<Book title='CSS is awesome' />

However, that quickly becomes a struggle to maintain. So let's look at how we could dynamically load these books from a list.

Creating a list in React

Open up your App.js and add a list like so above your app declaration.

const books = [
  {
    id: 1,
    title: 'Laravel collections',
  },
  {
    id: 2,
    title: 'Ruby for beginners',
  },
  {
    id: 3,
    title: 'CSS is awesome',
  },
];

function App() {}

We can leverage the' map' function to render these elements in our React app.

<Bookshelf>
  {books.map((book) => (
    <Book title={book.title} />
  ))}
</Bookshelf>

And this little piece of code will do the same thing as before.

Keys in React

However, I made one big mistake in the example above. When we render list items in React as we do above, we should always set a key property. This key will help React identify which items change or should be removed.

To add the key, we can use the following code.

<Book title={book.title} key={book.id} />

However, sometimes we do not have a key, so what do we do then?

Well, no worries, React comes with a built-in index we can use as the key.

const numbers = [1, 2, 3];

{
  numbers.map((number, index) => <span key={index}>Number: {number}</span>);
}

As you can see, the index is available on the map function as the unique key for each element.

You can find this code on GitHub. I hope you enjoyed this article about loops in React.

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