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@gaearon @clemmy
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fragments
Fragments
docs/fragments.html

A common pattern in React is for a component to return multiple elements. Fragments let you group a list of children without adding extra nodes to the DOM.

render() {
  return (
    <React.Fragment>
      <ChildA />
      <ChildB />
      <ChildC />
    </React.Fragment>
  );
}

There is also a new short syntax for declaring them, but it isn't supported by all popular tools yet.

Motivation

A common pattern is for a component to return a list of children. Take this example React snippet:

class Table extends React.Component {
  render() {
    return (
      <table>
        <tr>
          <Columns />
        </tr>
      </table>
    );
  }
}

<Columns /> would need to return multiple <td> elements in order for the rendered HTML to be valid. If a parent div was used inside the render() of <Columns />, then the resulting HTML will be invalid.

class Columns extends React.Component {
  render() {
    return (
      <div>
        <td>Hello</td>
        <td>World</td>
      </div>
    );
  }
}

results in a <Table /> output of:

<table>
  <tr>
    <div>
      <td>Hello</td>
      <td>World</td>
    </div>
  </tr>
</table>

So, we introduce Fragments.

Usage

class Columns extends React.Component {
  render() {
    return (
      <React.Fragment>
        <td>Hello</td>
        <td>World</td>
      </React.Fragment>
    );
  }
}

which results in a correct <Table /> output of:

<table>
  <tr>
    <td>Hello</td>
    <td>World</td>
  </tr>
</table>

Short Syntax

There is a new, shorter syntax you can use for declaring fragments. It looks like empty tags:

class Columns extends React.Component {
  render() {
    return (
      <>
        <td>Hello</td>
        <td>World</td>
      </>
    );
  }
}

You can use <></> the same way you'd use any other element except that it doesn't support keys or attributes.

Note that many tools don't support it yet so you might want to explicitly write <React.Fragment> until the tooling catches up.

Keyed Fragments

Fragments declared with the explicit <React.Fragment> syntax may have keys. A use case for this is mapping a collection to an array of fragments -- for example, to create a description list:

function Glossary(props) {
  return (
    <dl>
      {props.items.map(item => (
        // Without the `key`, React will fire a key warning
        <React.Fragment key={item.id}>
          <dt>{item.term}</dt>
          <dd>{item.description}</dd>
        </React.Fragment>
      ))}
    </dl>
  );
}

key is the only attribute that can be passed to Fragment. In the future, we may add support for additional attributes, such as event handlers.

Live Demo

You can try out the new JSX fragment syntax with this CodePen.