no-useless-fragment
Rule category
Correctness.
What it does
Prevents the use of useless fragments.
Why is this bad?
A fragment is redundant if it contains only one child, or if it is the child of a html element, and is not a keyed fragment.
Moreoever, rendering fragments with multiple levels of depth can cause React to not retain the state of components nested within the fragment after certain re-renders, which may lead to unexpected state resetting.
Examples
Failing
<><Foo /></>
<p><>foo</></p>
<></>
<section>
<>
<div />
<div />
</>
</section>Passing
{foo}
<Foo />
<>
<Foo />
<Bar />
</>
<>foo {bar}</>
<> {foo}</>
<>{children}</>
<>{props.children}</>
const cat = <>meow</>
<SomeComponent>
<>
<div />
<div />
</>
</SomeComponent>
<Fragment key={item.id}>{item.value}</Fragment>Note
By default, this rule always allows single expressions in a fragment. This is useful in
places like Typescript where string does not satisfy the expected return type
of JSX.Element. A common workaround is to wrap the variable holding a string
in a fragment and expression. To change this behaviour, use the allowExpressions option.
Examples of correct code for single expressions in fragments:
<>{foo}</>
<Fragment>{foo}</Fragment>Examples with allowExpressions: false
Failing
<><Foo /></>
<p><>foo</></p>
<></>
<Foo bar={<>baz</>} />
<section>
<>
<div />
<div />
</>
</section>
const cat = <>meow</>
<>{children}</>
<>{props.children}</>
<> {foo}</>
<SomeComponent>
<>
<div />
<div />
</>
</SomeComponent>Passing
{foo}
<Foo />
<>
<Foo />
<Bar />
</>
<>foo {bar}</>
<Fragment key={item.id}>{item.value}</Fragment>