Function addTransitionClass

static/vuejs/vue.common.js:6256–6259

(el, cls)

}

function addTransitionClass (el, cls) {
  (el._transitionClasses || (el._transitionClasses = [])).push(cls);
  addClass(el, cls);
}

function removeTransitionClass (el, cls) {
  if (el._transitionClasses) {