Support <> standalone fragment syntax

[smrq]

This syntax (or similar) has been brought up in a number of comments across various issues already, but as far as I can tell has no standalone proposal.

The syntax is:

<>
  <Child />
  <Child />
  <Child />
</>

This is equivalent to an array, except that because the structure of the array is statically known, keys could be automatically assigned to each child.

I think a lot of people may mistakenly think React 16.x can already do this as a result of the new feature to return multiple components from render. I suspect the lack of this syntax might become even more of a pain point with that release.

(Correct me if I'm wrong or should clarify anything further. I'm just making the issue because it seems there should have been one already.)

[gaearon]

cc @SanderSpies, if I recall you have something like this in Reason. How did it work out?

[diligiant]

@smrq let me reverse position (not the devil's advocate ;) here and say that React 16.x now allows us to do that (by explicitely setting key= in <Child />) ; BUT lots of us would like this to be implicit for the sake of new "users".

[sebmarkbage]

The key thing is one issue that follows a very specific heuristic. It may not be enough to warrant new syntax. It might be possible to find other ways.

The more convincing argument to me is the ability to nest text content and dropping the comma separator.

return <>
  Hello <strong>World</strong>!
</>

vs.

return [
  "Hello ", <strong>World</strong>, "!"
]

Another variant would be to drop the comma between JSX elements in arrays. This doesn't solve the text content issue though. Maybe that's just an argument for dropping JSXText #35?

return [
  <Foo />
  <Bar />
  <Baz />
]

vs.

return [
  <Foo />,
  <Bar />,
  <Baz />,
]

[sebmarkbage]

One thing that would be neat is that you sometimes would like to put a key on a whole fragment.

var dynamicList = items.map(item => {
  if (item.type === Foo) {
    return <>
      <Foo />
      <Bar />
    </>;
  }
  return <Foo key={item.id} />;
});

In the proposed <> syntax there is no syntactic space to define a key. If you put something in there such as "frag" then there is.

var dynamicList = items.map(item => {
  if (item.type === Foo) {
    return <Frag key={item.id}>
      <Foo />
      <Bar />
    </Frag>;
  }
  return <Foo key={item.id} />;
});

This can be implemented today in React as a component.

[dead-claudia]

I'll also point out that non-React usage of this would also greatly benefit (like Mithril + @jsx m, where Mithril already supports fragments).

[wmertens]

The issue with Frag is that it is in the same namespace as regular components.

How about <[]>…</[]>? => <[] key="foo">…</[]>

Or this might work: <{...{key: 'foo'}}>…</>

[ljharb]

What about something like <fragment />, which would be a host component that React could define?

[gaearon]

Another proposal was to use namespaces.

<react:fragment>
  <Child />
  <Child />
</react:fragment>

But if we were to do this, should we go all-in? For example key and ref are also React-specific (and technically don’t become props) so we could also do

<div react:key="1" react:ref={fn} />

But this is awkward to assign when defining element config as plain object.

[gaearon]

What about something like <fragment />, which would be a host component that React could define?

This blocks HTML from ever defining it. Kind of like MooTools killed [].contains().

[ljharb]

document.createDocumentFragment() already exists and HTML is highly unlikely to ever define <fragment>, but fair point 😬

I like the namespacing idea.

[gaearon]

A few more ideas.

<@fragment>
  <Child />
  <Child />
</@fragment>

<$>
  <Child />
  <Child />
</$>

[wmertens]

Or, use <> and when you do need to add a key, do-it-yourself:

const Frag = ({children}) => children

React could provide this as a named export of course.

I really like how obvious the <> syntax is. OTOH. It prevents<> being defined as a JS operator at some point.

[gaearon]

I like this.

<*>
  <Child />
  <Child />
</*>

It kind of implies "multiple elements" and you can put a key on it if you want.

var dynamicList = items.map(item => {
  if (item.type === Foo) {
    return (
      <* key={item.id}>
        <Foo />
        <Bar />
      </*>
    );
  }
  return <Foo key={item.id} />;
});

[gaearon]

Haha I guess that won't work because of comments 😛