Vue version

3.2.47

Link to minimal reproduction

https://play.vuejs.org/#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

Steps to reproduce

When there is no #default, there is a difference between the two behaviors

What is expected?

Consistent behavior when there is no #default

What is actually happening?

#default is right.

System Info

No response

Any additional comments?

No response

$slot.header returns a function. That function, when called, will render the slot content. if there's no slot content, it will return undefined

v-if="$slot.header()"

Be aware that:

1. This can have a certain runtime cost as the slot function is essentially a render function creating the vdom for the slot content, which can be relatively expensive if the slot contant is really large.
2. Slots sometimes can be "empty" at first glance from but technically still contain an empty Fragment vnode, so checking for undefined wil not necessarily alway be successul:

<your-component>
{{ isCondiotion ? 'yes' : undefined }} //this will lead to a Fragment.
</you-component>

If you need further help, please use Discussions or Discord to ask the community for help.

I don't think it solved this problem. You can take a look at this link, which provides a more concise description of my problem: https://play.vuejs.org/#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

why does it return undefined?

Why does it return function?