<Fragment> (<>...</>)

<Fragment>, often used via <>...</> syntax, lets you group elements without a wrapper node.

<>
  <OneChild />
  <AnotherChild />
</>

Viite
- <Fragment>
Käyttö

Viite

`<Fragment>`

Wrap elements in <Fragment> to group them together in situations where you need a single element. Grouping elements in Fragment has no effect on the resulting DOM; it is the same as if the elements were not grouped. The empty JSX tag <></> is shorthand for <Fragment></Fragment> in most cases.

Propsit

optional key: Fragments declared with the explicit <Fragment> syntax may have keys.

Rajoitukset

If you want to pass key to a Fragment, you can’t use the <>...</> syntax. You have to explicitly import Fragment from 'react' and render <Fragment key={yourKey}>...</Fragment>.
React does not reset state when you go from rendering <><Child /></> to [<Child />] or back, or when you go from rendering <><Child /></> to <Child /> and back. This only works a single level deep: for example, going from <><><Child /></></> to <Child /> resets the state. See the precise semantics here.

Käyttö

Returning multiple elements

Use Fragment, or the equivalent <>...</> syntax, to group multiple elements together. You can use it to put multiple elements in any place where a single element can go. For example, a component can only return one element, but by using a Fragment you can group multiple elements together and then return them as a group:

function Post() {
  return (
    <>
      <PostTitle />
      <PostBody />
    </>
  );
}

Fragments are useful because grouping elements with a Fragment has no effect on layout or styles, unlike if you wrapped the elements in another container like a DOM element. If you inspect this example with the browser tools, you’ll see that all <h1> and <article> DOM nodes appear as siblings without wrappers around them:

Forkkaa

export default function Blog() {
  return (
    <>
      <Post title="An update" body="It's been a while since I posted..." />
      <Post title="My new blog" body="I am starting a new blog!" />
    </>
  )
}

function Post({ title, body }) {
  return (
    <>
      <PostTitle title={title} />
      <PostBody body={body} />
    </>
  );
}

function PostTitle({ title }) {
  return <h1>{title}</h1>
}

function PostBody({ body }) {
  return (
    <article>
      <p>{body}</p>
    </article>
  );
}

Syväsukellus

How to write a Fragment without the special syntax?

The example above is equivalent to importing Fragment from React:

import { Fragment } from 'react';

function Post() {
  return (
    <Fragment>
      <PostTitle />
      <PostBody />
    </Fragment>
  );
}

Usually you won’t need this unless you need to pass a key to your Fragment.

Assigning multiple elements to a variable

Like any other element, you can assign Fragment elements to variables, pass them as props, and so on:

function CloseDialog() {
  const buttons = (
    <>
      <OKButton />
      <CancelButton />
    </>
  );
  return (
    <AlertDialog buttons={buttons}>
      Are you sure you want to leave this page?
    </AlertDialog>
  );
}

Grouping elements with text

You can use Fragment to group text together with components:

function DateRangePicker({ start, end }) {
  return (
    <>
      From
      <DatePicker date={start} />
      to
      <DatePicker date={end} />
    </>
  );
}

Rendering a list of Fragments

Here’s a situation where you need to write Fragment explicitly instead of using the <></> syntax. When you render multiple elements in a loop, you need to assign a key to each element. If the elements within the loop are Fragments, you need to use the normal JSX element syntax in order to provide the key attribute:

function Blog() {
  return posts.map(post =>
    <Fragment key={post.id}>
      <PostTitle title={post.title} />
      <PostBody body={post.body} />
    </Fragment>
  );
}

You can inspect the DOM to verify that there are no wrapper elements around the Fragment children:

Forkkaa

import { Fragment } from 'react';

const posts = [
  { id: 1, title: 'An update', body: "It's been a while since I posted..." },
  { id: 2, title: 'My new blog', body: 'I am starting a new blog!' }
];

export default function Blog() {
  return posts.map(post =>
    <Fragment key={post.id}>
      <PostTitle title={post.title} />
      <PostBody body={post.body} />
    </Fragment>
  );
}

function PostTitle({ title }) {
  return <h1>{title}</h1>
}

function PostBody({ body }) {
  return (
    <article>
      <p>{body}</p>
    </article>
  );
}

PreviousKomponentit Next<Profiler>