Function setup

packages/runtime-core/src/components/BaseTransition.ts:152–275

(props: BaseTransitionProps, { slots }: SetupContext)

  props: BaseTransitionPropsValidators,

  setup(props: BaseTransitionProps, { slots }: SetupContext) {
    const instance = getCurrentInstance()!
    const state = useTransitionState()

    return () => {
      const children =
        slots.default && getTransitionRawChildren(slots.default(), true)
      const child =
        children && children.length
          ? findNonCommentChild(children)
          : // Keep explicit default-slot conditionals on the same transition path
            // as regular v-if branches, which render a comment placeholder.
            instance.subTree
            ? createCommentVNode()
            : undefined
      if (!child) {
        return
      }

      // there's no need to track reactivity for these props so use the raw
      // props for a bit better perf
      const rawProps = toRaw(props)
      const { mode } = rawProps
      // check mode
      if (
        __DEV__ &&
        mode &&
        mode !== 'in-out' &&
        mode !== 'out-in' &&
        mode !== 'default'
      ) {
        warn(`invalid <transition> mode: ${mode}`)
      }

      if (state.isLeaving) {
        return emptyPlaceholder(child)
      }

      // in the case of <transition><keep-alive/></transition>, we need to
      // compare the type of the kept-alive children.
      const innerChild = getInnerChild(child)
      if (!innerChild) {
        return emptyPlaceholder(child)
      }

      let enterHooks = resolveTransitionHooks(
        innerChild,
        rawProps,
        state,
        instance,
        // #11061, ensure enterHooks is fresh after clone
        hooks => (enterHooks = hooks),
      )

      if (innerChild.type !== Comment) {
        setTransitionHooks(innerChild, enterHooks)
      }