React Lists
In React, you will render lists with some type of loop.
The JavaScript map() array method is generally the preferred
method.
If you need a refresher on the map() method, check out the
ES6 section.
Example:
Let's render all of the cars from our garage:
function Car(props) {
return <li>I am a { props.brand }</li>;
}
function Garage() {
const cars = ['Ford', 'BMW', 'Audi'];
return (
<>
<h1>Who lives in my garage?</h1>
<ul>
{cars.map((car) => <Car brand={car} />)}
</ul>
</>
);
}
const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<Garage />);
When you run this code in your create-react-app, it will work but you will
receive a warning that there is no "key" provided for the list items.
Keys
Keys allow React to keep track of elements. This way, if an item is updated or removed, only that item will be re-rendered instead of the entire list.
Keys need to be unique to each sibling. But they can be duplicated globally.
Generally, the key should be a unique ID assigned to each item. As a last resort, you can use the array index as a key.
Example:
Let's refactor our previous example to include keys:
function Car(props) {
return <li>I am a { props.brand }</li>;
}
function Garage() {
const cars = [
{id: 1, brand: 'Ford'},
{id: 2, brand: 'BMW'},
{id: 3, brand: 'Audi'}
];
return (
<>
<h1>Who lives in my garage?</h1>
<ul>
{cars.map((car) => <Car key={car.id} brand={car.brand} />)}
</ul>
</>
);
}
const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<Garage />);