One of the advantages of using React to render a user interface is that it’s easy to break up the UI into components. However, a common problem that arises is when we want to return sibling elements with no parent. React has a feature called Fragments that provides the solution.
The problem
If you aren’t familiar with the problem, consider this example.
function FAQ() {
return (
<p>Q. What is React?</p>
<p>A. A JavaScript library for building user interfaces</p>
<p>Q. How do I render sibling elements?</p>
<p>A. Use Fragments</p>
);
}
This code results in an error: Adjacent JSX elements must be wrapped in an enclosing tag.
The solutions
One option is to wrap the elements with a parent element.
function FAQ() {
return (
<div>
<p>Q. What is React?</p>
<p>A. A JavaScript library for building user interfaces</p>
<p>Q. How do I render sibling elements?</p>
<p>A. Use Fragments</p>
</div>
);
}
But this method introduces an extraneous element into the DOM, adding an extra level of nesting that we don’t actually need.
React v16.0 introduced another option, which is to return an array of elements.
function FAQ() {
return [
<p>Q. What is React?</p>,
<p>A. A JavaScript library for building user interfaces</p>,
<p>Q. How do I render sibling elements?</p>,
<p>A. Use Fragments</p>
];
}
Now we need to add commas in between elements. More importantly, this code produces a key warning: Warning: Each child in a list should have a unique "key" prop. Adding a key to every element fixes the issue but is quite cumbersome.
function FAQ() {
return [
<p key="q1">Q. What is React?</p>,
<p key="a1">A. A JavaScript library for building user interfaces</p>,
<p key="q2">Q. How do I render sibling elements?</p>,
<p key="a2">A. Use Fragments</p>
];
}
React v16.2 gave us a cleaner solution, which is to use Fragments.
function FAQ() {
return (
<React.Fragment>
<p>Q. What is React?</p>
<p>A. A JavaScript library for building user interfaces</p>
<p>Q. How do I render sibling elements?</p>
<p>A. Use Fragments</p>
</React.Fragment>
);
}
We no longer need to provide keys, we don’t need to add array commas, and we still avoid adding an extraneous DOM element because React.Fragment doesn’t become an actual element during rendering.
We can import Fragment to avoid having to fully write out React.Fragment.
import React, {Fragment} from "react";
function FAQ() {
return (
<Fragment>
<p>Q. What is React?</p>
<p>A. A JavaScript library for building user interfaces</p>
<p>Q. How do I render sibling elements?</p>
<p>A. Use Fragments</p>
</Fragment>
);
}
However, an even better method is to use the shorthand syntax for Fragments, which looks like empty tags: <> and </>.
function FAQ() {
return (
<>
<p>Q. What is React?</p>
<p>A. A JavaScript library for building user interfaces</p>
<p>Q. How do I render sibling elements?</p>
<p>A. Use Fragments</p>
</>
);
}
This gives us the same benefits as using React.Fragment, but we don’t need to import anything else, and our code looks cleaner.
The only thing that the shorthand syntax doesn’t support for now is adding a key. This could be problematic if you are creating a description list, for example. In this case, use the standard syntax.
function Dictionary(props) {
return (
<dl>
{props.terms.map(({word, definition}) =>
<React.Fragment key={word}>
<dt>{word}</dt>
<dd>{definition}</dd>
</React.Fragment>
)}
</dl>
);
}
We need to provide a key to avoid a key warning.
In most cases, however, the shorthand method is the best solution for our original problem of returning sibling elements. This solution has worked out well enough that Vue.js will also natively support the concept of Fragments when v3 is released.
Using Fragments
In the last two years, the JavaScript ecosystem has added widespread support for Fragments.
- React added support for the shorthand syntax in version 16.2.0 (November 28, 2017)
- TypeScript added support in version 2.6.2 (November 27, 2017)
- Babel added support in version 7 (August 27, 2018)
- Prettier added support in version 1.9 (December 5, 2017)
- eslint-plugin-react added a jsx-fragments rule in version 7.12.0 (December 28, 2018) to enforce using the standard or shorthand syntax
If you upgrade your dependencies, you will probably be able to use Fragments without any additional configuration.
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