Nuxt/packages/vue-app/template/components/nuxt-child.js

<%= isTest ? '// @vue/component' : '' %>
export default {
  name: 'NuxtChild',
  functional: true,
  props: {
    nuxtChildKey: {
      type: String,
      default: ''
    },
    keepAlive: Boolean,
    keepAliveProps: {
      type: Object,
      default: undefined
    }
  },
  render(h, { parent, data, props }) {
    data.nuxtChild = true
    const _parent = parent
    const transitions = parent.<%= globals.nuxt %>.nuxt.transitions
    const defaultTransition = parent.<%= globals.nuxt %>.nuxt.defaultTransition

    let depth = 0
    while (parent) {
      if (parent.$vnode && parent.$vnode.data.nuxtChild) {
        depth++
      }
      parent = parent.$parent
    }
    data.nuxtChildDepth = depth
    const transition = transitions[depth] || defaultTransition
    const transitionProps = {}
    transitionsKeys.forEach((key) => {
      if (typeof transition[key] !== 'undefined') {
        transitionProps[key] = transition[key]
      }
    })

    const listeners = {}
    listenersKeys.forEach((key) => {
      if (typeof transition[key] === 'function') {
        listeners[key] = transition[key].bind(_parent)
      }
    })
    // Add triggerScroll event on beforeEnter (fix #1376)
    const beforeEnter = listeners.beforeEnter
    listeners.beforeEnter = (el) => {
      // Ensure to trigger scroll event after calling scrollBehavior
      window.<%= globals.nuxt %>.$nextTick(() => {
        window.<%= globals.nuxt %>.$emit('triggerScroll')
      })
      if (beforeEnter) {
        return beforeEnter.call(_parent, el)
      }
    }

    // make sure that leave is called asynchronous (fix #5703)
    if (transition.css === false) {
      const leave = listeners.leave
      listeners.leave = (el, done) => {
        if (leave) {
          leave.call(_parent, el)
        }

        _parent.$nextTick(done)
      }
    }

    let routerView = h('routerView', data)

    if (props.keepAlive) {
      routerView = h('keep-alive', { props: props.keepAliveProps }, [routerView])
    }

    return h('transition', {
      props: transitionProps,
      on: listeners
    }, [routerView])
  }
}

const transitionsKeys = [
  'name',
  'mode',
  'appear',
  'css',
  'type',
  'duration',
  'enterClass',
  'leaveClass',
  'appearClass',
  'enterActiveClass',
  'enterActiveClass',
  'leaveActiveClass',
  'appearActiveClass',
  'enterToClass',
  'leaveToClass',
  'appearToClass'
]

const listenersKeys = [
  'beforeEnter',
  'enter',
  'afterEnter',
  'enterCancelled',
  'beforeLeave',
  'leave',
  'afterLeave',
  'leaveCancelled',
  'beforeAppear',
  'appear',
  'afterAppear',
  'appearCancelled'
]