switch to vuepress

7 files changed, 799 insertions, 0 deletions

diff --git a/node_modules/vue/src/platforms/web/runtime/modules/attrs.js b/node_modules/vue/src/platforms/web/runtime/modules/attrs.js
new file mode 100644
index 00000000..78ef28a1
--- /dev/null
+++ b/node_modules/vue/src/platforms/web/runtime/modules/attrs.js
@@ -0,0 +1,118 @@
+/* @flow */
+
+import { isIE, isIE9, isEdge } from 'core/util/env'
+
+import {
+  extend,
+  isDef,
+  isUndef
+} from 'shared/util'
+
+import {
+  isXlink,
+  xlinkNS,
+  getXlinkProp,
+  isBooleanAttr,
+  isEnumeratedAttr,
+  isFalsyAttrValue
+} from 'web/util/index'
+
+function updateAttrs (oldVnode: VNodeWithData, vnode: VNodeWithData) {
+  const opts = vnode.componentOptions
+  if (isDef(opts) && opts.Ctor.options.inheritAttrs === false) {
+    return
+  }
+  if (isUndef(oldVnode.data.attrs) && isUndef(vnode.data.attrs)) {
+    return
+  }
+  let key, cur, old
+  const elm = vnode.elm
+  const oldAttrs = oldVnode.data.attrs || {}
+  let attrs: any = vnode.data.attrs || {}
+  // clone observed objects, as the user probably wants to mutate it
+  if (isDef(attrs.__ob__)) {
+    attrs = vnode.data.attrs = extend({}, attrs)
+  }
+
+  for (key in attrs) {
+    cur = attrs[key]
+    old = oldAttrs[key]
+    if (old !== cur) {
+      setAttr(elm, key, cur)
+    }
+  }
+  // #4391: in IE9, setting type can reset value for input[type=radio]
+  // #6666: IE/Edge forces progress value down to 1 before setting a max
+  /* istanbul ignore if */
+  if ((isIE || isEdge) && attrs.value !== oldAttrs.value) {
+    setAttr(elm, 'value', attrs.value)
+  }
+  for (key in oldAttrs) {
+    if (isUndef(attrs[key])) {
+      if (isXlink(key)) {
+        elm.removeAttributeNS(xlinkNS, getXlinkProp(key))
+      } else if (!isEnumeratedAttr(key)) {
+        elm.removeAttribute(key)
+      }
+    }
+  }
+}
+
+function setAttr (el: Element, key: string, value: any) {
+  if (el.tagName.indexOf('-') > -1) {
+    baseSetAttr(el, key, value)
+  } else if (isBooleanAttr(key)) {
+    // set attribute for blank value
+    // e.g. <option disabled>Select one</option>
+    if (isFalsyAttrValue(value)) {
+      el.removeAttribute(key)
+    } else {
+      // technically allowfullscreen is a boolean attribute for <iframe>,
+      // but Flash expects a value of "true" when used on <embed> tag
+      value = key === 'allowfullscreen' && el.tagName === 'EMBED'
+        ? 'true'
+        : key
+      el.setAttribute(key, value)
+    }
+  } else if (isEnumeratedAttr(key)) {
+    el.setAttribute(key, isFalsyAttrValue(value) || value === 'false' ? 'false' : 'true')
+  } else if (isXlink(key)) {
+    if (isFalsyAttrValue(value)) {
+      el.removeAttributeNS(xlinkNS, getXlinkProp(key))
+    } else {
+      el.setAttributeNS(xlinkNS, key, value)
+    }
+  } else {
+    baseSetAttr(el, key, value)
+  }
+}
+
+function baseSetAttr (el, key, value) {
+  if (isFalsyAttrValue(value)) {
+    el.removeAttribute(key)
+  } else {
+    // #7138: IE10 & 11 fires input event when setting placeholder on
+    // <textarea>... block the first input event and remove the blocker
+    // immediately.
+    /* istanbul ignore if */
+    if (
+      isIE && !isIE9 &&
+      el.tagName === 'TEXTAREA' &&
+      key === 'placeholder' && !el.__ieph
+    ) {
+      const blocker = e => {
+        e.stopImmediatePropagation()
+        el.removeEventListener('input', blocker)
+      }
+      el.addEventListener('input', blocker)
+      // $flow-disable-line
+      el.__ieph = true /* IE placeholder patched */
+    }
+    el.setAttribute(key, value)
+  }
+}
+
+export default {
+  create: updateAttrs,
+  update: updateAttrs
+}
diff --git a/node_modules/vue/src/platforms/web/runtime/modules/class.js b/node_modules/vue/src/platforms/web/runtime/modules/class.js
new file mode 100644
index 00000000..29fd2c11
--- /dev/null
+++ b/node_modules/vue/src/platforms/web/runtime/modules/class.js
@@ -0,0 +1,48 @@
+/* @flow */
+
+import {
+  isDef,
+  isUndef
+} from 'shared/util'
+
+import {
+  concat,
+  stringifyClass,
+  genClassForVnode
+} from 'web/util/index'
+
+function updateClass (oldVnode: any, vnode: any) {
+  const el = vnode.elm
+  const data: VNodeData = vnode.data
+  const oldData: VNodeData = oldVnode.data
+  if (
+    isUndef(data.staticClass) &&
+    isUndef(data.class) && (
+      isUndef(oldData) || (
+        isUndef(oldData.staticClass) &&
+        isUndef(oldData.class)
+      )
+    )
+  ) {
+    return
+  }
+
+  let cls = genClassForVnode(vnode)
+
+  // handle transition classes
+  const transitionClass = el._transitionClasses
+  if (isDef(transitionClass)) {
+    cls = concat(cls, stringifyClass(transitionClass))
+  }
+
+  // set the class
+  if (cls !== el._prevClass) {
+    el.setAttribute('class', cls)
+    el._prevClass = cls
+  }
+}
+
+export default {
+  create: updateClass,
+  update: updateClass
+}
diff --git a/node_modules/vue/src/platforms/web/runtime/modules/dom-props.js b/node_modules/vue/src/platforms/web/runtime/modules/dom-props.js
new file mode 100644
index 00000000..f3888aed
--- /dev/null
+++ b/node_modules/vue/src/platforms/web/runtime/modules/dom-props.js
@@ -0,0 +1,95 @@
+/* @flow */
+
+import { isDef, isUndef, extend, toNumber } from 'shared/util'
+
+function updateDOMProps (oldVnode: VNodeWithData, vnode: VNodeWithData) {
+  if (isUndef(oldVnode.data.domProps) && isUndef(vnode.data.domProps)) {
+    return
+  }
+  let key, cur
+  const elm: any = vnode.elm
+  const oldProps = oldVnode.data.domProps || {}
+  let props = vnode.data.domProps || {}
+  // clone observed objects, as the user probably wants to mutate it
+  if (isDef(props.__ob__)) {
+    props = vnode.data.domProps = extend({}, props)
+  }
+
+  for (key in oldProps) {
+    if (isUndef(props[key])) {
+      elm[key] = ''
+    }
+  }
+  for (key in props) {
+    cur = props[key]
+    // ignore children if the node has textContent or innerHTML,
+    // as these will throw away existing DOM nodes and cause removal errors
+    // on subsequent patches (#3360)
+    if (key === 'textContent' || key === 'innerHTML') {
+      if (vnode.children) vnode.children.length = 0
+      if (cur === oldProps[key]) continue
+      // #6601 work around Chrome version <= 55 bug where single textNode
+      // replaced by innerHTML/textContent retains its parentNode property
+      if (elm.childNodes.length === 1) {
+        elm.removeChild(elm.childNodes[0])
+      }
+    }
+
+    if (key === 'value') {
+      // store value as _value as well since
+      // non-string values will be stringified
+      elm._value = cur
+      // avoid resetting cursor position when value is the same
+      const strCur = isUndef(cur) ? '' : String(cur)
+      if (shouldUpdateValue(elm, strCur)) {
+        elm.value = strCur
+      }
+    } else {
+      elm[key] = cur
+    }
+  }
+}
+
+// check platforms/web/util/attrs.js acceptValue
+type acceptValueElm = HTMLInputElement | HTMLSelectElement | HTMLOptionElement;
+
+function shouldUpdateValue (elm: acceptValueElm, checkVal: string): boolean {
+  return (!elm.composing && (
+    elm.tagName === 'OPTION' ||
+    isNotInFocusAndDirty(elm, checkVal) ||
+    isDirtyWithModifiers(elm, checkVal)
+  ))
+}
+
+function isNotInFocusAndDirty (elm: acceptValueElm, checkVal: string): boolean {
+  // return true when textbox (.number and .trim) loses focus and its value is
+  // not equal to the updated value
+  let notInFocus = true
+  // #6157
+  // work around IE bug when accessing document.activeElement in an iframe
+  try { notInFocus = document.activeElement !== elm } catch (e) {}
+  return notInFocus && elm.value !== checkVal
+}
+
+function isDirtyWithModifiers (elm: any, newVal: string): boolean {
+  const value = elm.value
+  const modifiers = elm._vModifiers // injected by v-model runtime
+  if (isDef(modifiers)) {
+    if (modifiers.lazy) {
+      // inputs with lazy should only be updated when not in focus
+      return false
+    }
+    if (modifiers.number) {
+      return toNumber(value) !== toNumber(newVal)
+    }
+    if (modifiers.trim) {
+      return value.trim() !== newVal.trim()
+    }
+  }
+  return value !== newVal
+}
+
+export default {
+  create: updateDOMProps,
+  update: updateDOMProps
+}
diff --git a/node_modules/vue/src/platforms/web/runtime/modules/events.js b/node_modules/vue/src/platforms/web/runtime/modules/events.js
new file mode 100644
index 00000000..1e71b667
--- /dev/null
+++ b/node_modules/vue/src/platforms/web/runtime/modules/events.js
@@ -0,0 +1,87 @@
+/* @flow */
+
+import { isDef, isUndef } from 'shared/util'
+import { updateListeners } from 'core/vdom/helpers/index'
+import { withMacroTask, isIE, supportsPassive } from 'core/util/index'
+import { RANGE_TOKEN, CHECKBOX_RADIO_TOKEN } from 'web/compiler/directives/model'
+
+// normalize v-model event tokens that can only be determined at runtime.
+// it's important to place the event as the first in the array because
+// the whole point is ensuring the v-model callback gets called before
+// user-attached handlers.
+function normalizeEvents (on) {
+  /* istanbul ignore if */
+  if (isDef(on[RANGE_TOKEN])) {
+    // IE input[type=range] only supports `change` event
+    const event = isIE ? 'change' : 'input'
+    on[event] = [].concat(on[RANGE_TOKEN], on[event] || [])
+    delete on[RANGE_TOKEN]
+  }
+  // This was originally intended to fix #4521 but no longer necessary
+  // after 2.5. Keeping it for backwards compat with generated code from < 2.4
+  /* istanbul ignore if */
+  if (isDef(on[CHECKBOX_RADIO_TOKEN])) {
+    on.change = [].concat(on[CHECKBOX_RADIO_TOKEN], on.change || [])
+    delete on[CHECKBOX_RADIO_TOKEN]
+  }
+}
+
+let target: any
+
+function createOnceHandler (handler, event, capture) {
+  const _target = target // save current target element in closure
+  return function onceHandler () {
+    const res = handler.apply(null, arguments)
+    if (res !== null) {
+      remove(event, onceHandler, capture, _target)
+    }
+  }
+}
+
+function add (
+  event: string,
+  handler: Function,
+  once: boolean,
+  capture: boolean,
+  passive: boolean
+) {
+  handler = withMacroTask(handler)
+  if (once) handler = createOnceHandler(handler, event, capture)
+  target.addEventListener(
+    event,
+    handler,
+    supportsPassive
+      ? { capture, passive }
+      : capture
+  )
+}
+
+function remove (
+  event: string,
+  handler: Function,
+  capture: boolean,
+  _target?: HTMLElement
+) {
+  (_target || target).removeEventListener(
+    event,
+    handler._withTask || handler,
+    capture
+  )
+}
+
+function updateDOMListeners (oldVnode: VNodeWithData, vnode: VNodeWithData) {
+  if (isUndef(oldVnode.data.on) && isUndef(vnode.data.on)) {
+    return
+  }
+  const on = vnode.data.on || {}
+  const oldOn = oldVnode.data.on || {}
+  target = vnode.elm
+  normalizeEvents(on)
+  updateListeners(on, oldOn, add, remove, vnode.context)
+  target = undefined
+}
+
+export default {
+  create: updateDOMListeners,
+  update: updateDOMListeners
+}
diff --git a/node_modules/vue/src/platforms/web/runtime/modules/index.js b/node_modules/vue/src/platforms/web/runtime/modules/index.js
new file mode 100644
index 00000000..9f6ad8f9
--- /dev/null
+++ b/node_modules/vue/src/platforms/web/runtime/modules/index.js
@@ -0,0 +1,15 @@
+import attrs from './attrs'
+import klass from './class'
+import events from './events'
+import domProps from './dom-props'
+import style from './style'
+import transition from './transition'
+
+export default [
+  attrs,
+  klass,
+  events,
+  domProps,
+  style,
+  transition
+]
diff --git a/node_modules/vue/src/platforms/web/runtime/modules/style.js b/node_modules/vue/src/platforms/web/runtime/modules/style.js
new file mode 100644
index 00000000..29e1c3c1
--- /dev/null
+++ b/node_modules/vue/src/platforms/web/runtime/modules/style.js
@@ -0,0 +1,93 @@
+/* @flow */
+
+import { getStyle, normalizeStyleBinding } from 'web/util/style'
+import { cached, camelize, extend, isDef, isUndef } from 'shared/util'
+
+const cssVarRE = /^--/
+const importantRE = /\s*!important$/
+const setProp = (el, name, val) => {
+  /* istanbul ignore if */
+  if (cssVarRE.test(name)) {
+    el.style.setProperty(name, val)
+  } else if (importantRE.test(val)) {
+    el.style.setProperty(name, val.replace(importantRE, ''), 'important')
+  } else {
+    const normalizedName = normalize(name)
+    if (Array.isArray(val)) {
+      // Support values array created by autoprefixer, e.g.
+      // {display: ["-webkit-box", "-ms-flexbox", "flex"]}
+      // Set them one by one, and the browser will only set those it can recognize
+      for (let i = 0, len = val.length; i < len; i++) {
+        el.style[normalizedName] = val[i]
+      }
+    } else {
+      el.style[normalizedName] = val
+    }
+  }
+}
+
+const vendorNames = ['Webkit', 'Moz', 'ms']
+
+let emptyStyle
+const normalize = cached(function (prop) {
+  emptyStyle = emptyStyle || document.createElement('div').style
+  prop = camelize(prop)
+  if (prop !== 'filter' && (prop in emptyStyle)) {
+    return prop
+  }
+  const capName = prop.charAt(0).toUpperCase() + prop.slice(1)
+  for (let i = 0; i < vendorNames.length; i++) {
+    const name = vendorNames[i] + capName
+    if (name in emptyStyle) {
+      return name
+    }
+  }
+})
+
+function updateStyle (oldVnode: VNodeWithData, vnode: VNodeWithData) {
+  const data = vnode.data
+  const oldData = oldVnode.data
+
+  if (isUndef(data.staticStyle) && isUndef(data.style) &&
+    isUndef(oldData.staticStyle) && isUndef(oldData.style)
+  ) {
+    return
+  }
+
+  let cur, name
+  const el: any = vnode.elm
+  const oldStaticStyle: any = oldData.staticStyle
+  const oldStyleBinding: any = oldData.normalizedStyle || oldData.style || {}
+
+  // if static style exists, stylebinding already merged into it when doing normalizeStyleData
+  const oldStyle = oldStaticStyle || oldStyleBinding
+
+  const style = normalizeStyleBinding(vnode.data.style) || {}
+
+  // store normalized style under a different key for next diff
+  // make sure to clone it if it's reactive, since the user likely wants
+  // to mutate it.
+  vnode.data.normalizedStyle = isDef(style.__ob__)
+    ? extend({}, style)
+    : style
+
+  const newStyle = getStyle(vnode, true)
+
+  for (name in oldStyle) {
+    if (isUndef(newStyle[name])) {
+      setProp(el, name, '')
+    }
+  }
+  for (name in newStyle) {
+    cur = newStyle[name]
+    if (cur !== oldStyle[name]) {
+      // ie9 setting to null has no effect, must use empty string
+      setProp(el, name, cur == null ? '' : cur)
+    }
+  }
+}
+
+export default {
+  create: updateStyle,
+  update: updateStyle
+}
diff --git a/node_modules/vue/src/platforms/web/runtime/modules/transition.js b/node_modules/vue/src/platforms/web/runtime/modules/transition.js
new file mode 100644
index 00000000..0796b5da
--- /dev/null
+++ b/node_modules/vue/src/platforms/web/runtime/modules/transition.js
@@ -0,0 +1,343 @@
+/* @flow */
+
+import { inBrowser, isIE9, warn } from 'core/util/index'
+import { mergeVNodeHook } from 'core/vdom/helpers/index'
+import { activeInstance } from 'core/instance/lifecycle'
+
+import {
+  once,
+  isDef,
+  isUndef,
+  isObject,
+  toNumber
+} from 'shared/util'
+
+import {
+  nextFrame,
+  resolveTransition,
+  whenTransitionEnds,
+  addTransitionClass,
+  removeTransitionClass
+} from '../transition-util'
+
+export function enter (vnode: VNodeWithData, toggleDisplay: ?() => void) {
+  const el: any = vnode.elm
+
+  // call leave callback now
+  if (isDef(el._leaveCb)) {
+    el._leaveCb.cancelled = true
+    el._leaveCb()
+  }
+
+  const data = resolveTransition(vnode.data.transition)
+  if (isUndef(data)) {
+    return
+  }
+
+  /* istanbul ignore if */
+  if (isDef(el._enterCb) || el.nodeType !== 1) {
+    return
+  }
+
+  const {
+    css,
+    type,
+    enterClass,
+    enterToClass,
+    enterActiveClass,
+    appearClass,
+    appearToClass,
+    appearActiveClass,
+    beforeEnter,
+    enter,
+    afterEnter,
+    enterCancelled,
+    beforeAppear,
+    appear,
+    afterAppear,
+    appearCancelled,
+    duration
+  } = data
+
+  // activeInstance will always be the <transition> component managing this
+  // transition. One edge case to check is when the <transition> is placed
+  // as the root node of a child component. In that case we need to check
+  // <transition>'s parent for appear check.
+  let context = activeInstance
+  let transitionNode = activeInstance.$vnode
+  while (transitionNode && transitionNode.parent) {
+    transitionNode = transitionNode.parent
+    context = transitionNode.context
+  }
+
+  const isAppear = !context._isMounted || !vnode.isRootInsert
+
+  if (isAppear && !appear && appear !== '') {
+    return
+  }
+
+  const startClass = isAppear && appearClass
+    ? appearClass
+    : enterClass
+  const activeClass = isAppear && appearActiveClass
+    ? appearActiveClass
+    : enterActiveClass
+  const toClass = isAppear && appearToClass
+    ? appearToClass
+    : enterToClass
+
+  const beforeEnterHook = isAppear
+    ? (beforeAppear || beforeEnter)
+    : beforeEnter
+  const enterHook = isAppear
+    ? (typeof appear === 'function' ? appear : enter)
+    : enter
+  const afterEnterHook = isAppear
+    ? (afterAppear || afterEnter)
+    : afterEnter
+  const enterCancelledHook = isAppear
+    ? (appearCancelled || enterCancelled)
+    : enterCancelled
+
+  const explicitEnterDuration: any = toNumber(
+    isObject(duration)
+      ? duration.enter
+      : duration
+  )
+
+  if (process.env.NODE_ENV !== 'production' && explicitEnterDuration != null) {
+    checkDuration(explicitEnterDuration, 'enter', vnode)
+  }
+
+  const expectsCSS = css !== false && !isIE9
+  const userWantsControl = getHookArgumentsLength(enterHook)
+
+  const cb = el._enterCb = once(() => {
+    if (expectsCSS) {
+      removeTransitionClass(el, toClass)
+      removeTransitionClass(el, activeClass)
+    }
+    if (cb.cancelled) {
+      if (expectsCSS) {
+        removeTransitionClass(el, startClass)
+      }
+      enterCancelledHook && enterCancelledHook(el)
+    } else {
+      afterEnterHook && afterEnterHook(el)
+    }
+    el._enterCb = null
+  })
+
+  if (!vnode.data.show) {
+    // remove pending leave element on enter by injecting an insert hook
+    mergeVNodeHook(vnode, 'insert', () => {
+      const parent = el.parentNode
+      const pendingNode = parent && parent._pending && parent._pending[vnode.key]
+      if (pendingNode &&
+        pendingNode.tag === vnode.tag &&
+        pendingNode.elm._leaveCb
+      ) {
+        pendingNode.elm._leaveCb()
+      }
+      enterHook && enterHook(el, cb)
+    })
+  }
+
+  // start enter transition
+  beforeEnterHook && beforeEnterHook(el)
+  if (expectsCSS) {
+    addTransitionClass(el, startClass)
+    addTransitionClass(el, activeClass)
+    nextFrame(() => {
+      removeTransitionClass(el, startClass)
+      if (!cb.cancelled) {
+        addTransitionClass(el, toClass)
+        if (!userWantsControl) {
+          if (isValidDuration(explicitEnterDuration)) {
+            setTimeout(cb, explicitEnterDuration)
+          } else {
+            whenTransitionEnds(el, type, cb)
+          }
+        }
+      }
+    })
+  }
+
+  if (vnode.data.show) {
+    toggleDisplay && toggleDisplay()
+    enterHook && enterHook(el, cb)
+  }
+
+  if (!expectsCSS && !userWantsControl) {
+    cb()
+  }
+}
+
+export function leave (vnode: VNodeWithData, rm: Function) {
+  const el: any = vnode.elm
+
+  // call enter callback now
+  if (isDef(el._enterCb)) {
+    el._enterCb.cancelled = true
+    el._enterCb()
+  }
+
+  const data = resolveTransition(vnode.data.transition)
+  if (isUndef(data) || el.nodeType !== 1) {
+    return rm()
+  }
+
+  /* istanbul ignore if */
+  if (isDef(el._leaveCb)) {
+    return
+  }
+
+  const {
+    css,
+    type,
+    leaveClass,
+    leaveToClass,
+    leaveActiveClass,
+    beforeLeave,
+    leave,
+    afterLeave,
+    leaveCancelled,
+    delayLeave,
+    duration
+  } = data
+
+  const expectsCSS = css !== false && !isIE9
+  const userWantsControl = getHookArgumentsLength(leave)
+
+  const explicitLeaveDuration: any = toNumber(
+    isObject(duration)
+      ? duration.leave
+      : duration
+  )
+
+  if (process.env.NODE_ENV !== 'production' && isDef(explicitLeaveDuration)) {
+    checkDuration(explicitLeaveDuration, 'leave', vnode)
+  }
+
+  const cb = el._leaveCb = once(() => {
+    if (el.parentNode && el.parentNode._pending) {
+      el.parentNode._pending[vnode.key] = null
+    }
+    if (expectsCSS) {
+      removeTransitionClass(el, leaveToClass)
+      removeTransitionClass(el, leaveActiveClass)
+    }
+    if (cb.cancelled) {
+      if (expectsCSS) {
+        removeTransitionClass(el, leaveClass)
+      }
+      leaveCancelled && leaveCancelled(el)
+    } else {
+      rm()
+      afterLeave && afterLeave(el)
+    }
+    el._leaveCb = null
+  })
+
+  if (delayLeave) {
+    delayLeave(performLeave)
+  } else {
+    performLeave()
+  }
+
+  function performLeave () {
+    // the delayed leave may have already been cancelled
+    if (cb.cancelled) {
+      return
+    }
+    // record leaving element
+    if (!vnode.data.show) {
+      (el.parentNode._pending || (el.parentNode._pending = {}))[(vnode.key: any)] = vnode
+    }
+    beforeLeave && beforeLeave(el)
+    if (expectsCSS) {
+      addTransitionClass(el, leaveClass)
+      addTransitionClass(el, leaveActiveClass)
+      nextFrame(() => {
+        removeTransitionClass(el, leaveClass)
+        if (!cb.cancelled) {
+          addTransitionClass(el, leaveToClass)
+          if (!userWantsControl) {
+            if (isValidDuration(explicitLeaveDuration)) {
+              setTimeout(cb, explicitLeaveDuration)
+            } else {
+              whenTransitionEnds(el, type, cb)
+            }
+          }
+        }
+      })
+    }
+    leave && leave(el, cb)
+    if (!expectsCSS && !userWantsControl) {
+      cb()
+    }
+  }
+}
+
+// only used in dev mode
+function checkDuration (val, name, vnode) {
+  if (typeof val !== 'number') {
+    warn(
+      `<transition> explicit ${name} duration is not a valid number - ` +
+      `got ${JSON.stringify(val)}.`,
+      vnode.context
+    )
+  } else if (isNaN(val)) {
+    warn(
+      `<transition> explicit ${name} duration is NaN - ` +
+      'the duration expression might be incorrect.',
+      vnode.context
+    )
+  }
+}
+
+function isValidDuration (val) {
+  return typeof val === 'number' && !isNaN(val)
+}
+
+/**
+ * Normalize a transition hook's argument length. The hook may be:
+ * - a merged hook (invoker) with the original in .fns
+ * - a wrapped component method (check ._length)
+ * - a plain function (.length)
+ */
+function getHookArgumentsLength (fn: Function): boolean {
+  if (isUndef(fn)) {
+    return false
+  }
+  const invokerFns = fn.fns
+  if (isDef(invokerFns)) {
+    // invoker
+    return getHookArgumentsLength(
+      Array.isArray(invokerFns)
+        ? invokerFns[0]
+        : invokerFns
+    )
+  } else {
+    return (fn._length || fn.length) > 1
+  }
+}
+
+function _enter (_: any, vnode: VNodeWithData) {
+  if (vnode.data.show !== true) {
+    enter(vnode)
+  }
+}
+
+export default inBrowser ? {
+  create: _enter,
+  activate: _enter,
+  remove (vnode: VNode, rm: Function) {
+    /* istanbul ignore else */
+    if (vnode.data.show !== true) {
+      leave(vnode, rm)
+    } else {
+      rm()
+    }
+  }
+} : {}