# Loops in JSX

More often than not we'll be dealing with lists and collections and not just simple singular items. That means we'll need to iterate over data, but there's no way to use `for` loops in JSX. Let's use `.map`.

```jsx
const App: React.FC = () => {
    const products: Product[] = [
        {
          name: "JavaScript: The Definitive Guide",
          description: `Since 1996, JavaScript: The Definitive Guide...`,
          price: 28.89
        },
        {
          name: "Eloquent JavaScript",
          description: `JavaScript lies at the heart...`,
          price: 21.22
        },
        {
          name: "JavaScript: The Good Parts",
          description: `Most programming languages...`,
          price: 16.59
        }
    ]

    return (
        <section>
            <h1>Products</h1>
            { products.map(product => (
                <div key={product.name}>
                    <header>{ product.name }</header>
                    <p>
                        { product.description }
                    </p>
                    <span>{ product.price }$</span>
                </div>
            )) }
        </section>
    )
}
```

Overall, quite straightforward: there's an array of items, over which we iterate using `.map` and return some JSX for each element. Similar to using components, each piece of JSX returned by the `.map` transformation must have exactly one root element.

There's also the `key` property on the root element of each product. This not *strictly* required (will work, React will just complain), but it allows React to easily distinguish between elements during the reconcilation process. Should be unique for each element in the array.

## Resources

* [Lists and keys](https://reactjs.org/docs/lists-and-keys.html)
* [Array.prototype.map()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map)
* [Reconcilation](https://reactjs.org/docs/reconciliation.html)
* [Index as a key is an anti-pattern](https://medium.com/@robinpokorny/index-as-a-key-is-an-anti-pattern-e0349aece318)
* [The significance of React keys - a visual explanation](https://dev.to/jtonzing/the-significance-of-react-keys---a-visual-explanation--56l7)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://okelm.gitbook.io/devmeetings-react-ts-fork/components-props/loops.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.