Function onBeforeEnter

packages/runtime-dom/src/components/Transition.ts:231–238

(el)

  return extend(baseProps, {
    onBeforeEnter(el) {
      callHook(onBeforeEnter, [el])
      addTransitionClass(el, enterFromClass)
      if (__COMPAT__ && legacyClassEnabled && legacyEnterFromClass) {
        addTransitionClass(el, legacyEnterFromClass)
      }
      addTransitionClass(el, enterActiveClass)
    },
    onBeforeAppear(el) {
      callHook(onBeforeAppear, [el])
      addTransitionClass(el, appearFromClass)