animate v-if with slide down/up transition (Vue.js 2)

Question

In my Vue app I have a simple toggle which renders a list when active. The list should not appear/disappear instantly. I want to have a smooth slide down transition on render and a smooth slide up transition on hide.

The following code shows what I have so far, does someone know how to make it work?

new Vue({
  el: '#app',
  data: () => ({
    isOpen: true,
  }),
});

.expand-enter-active,
.expand-leave-active {
  overflow: hidden;
  transition: height .5s linear;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>

<div id="app">
  <button @click="isOpen = !isOpen">
    is open: {{ isOpen }}
  </button>
  <transition name="expand">
    <div v-if="isOpen">
      <div>1</div>
      <div>2</div>
      <div>3</div>
    </div>
  </transition>
</div>

Answer 1

Please take a look this solution.

Vue.component('transition-collapse-height', {
  template: `<transition
    enter-active-class="enter-active"
    leave-active-class="leave-active"
    @before-enter="beforeEnter"
    @enter="enter"
    @after-enter="afterEnter"
    @before-leave="beforeLeave"
    @leave="leave"
    @after-leave="afterLeave"
  >
    <slot />
  </transition>`,
  methods: {
    /**
     * @param {HTMLElement} element
     */
    beforeEnter(element) {
      requestAnimationFrame(() => {
        if (!element.style.height) {
          element.style.height = '0px';
        }

        element.style.display = null;
      });
    },
    /**
     * @param {HTMLElement} element
     */
    enter(element) {
      requestAnimationFrame(() => {
        requestAnimationFrame(() => {
          element.style.height = `${element.scrollHeight}px`;
        });
      });
    },
    /**
     * @param {HTMLElement} element
     */
    afterEnter(element) {
      element.style.height = null;
    },
    /**
     * @param {HTMLElement} element
     */
    beforeLeave(element) {
      requestAnimationFrame(() => {
        if (!element.style.height) {
          element.style.height = `${element.offsetHeight}px`;
        }
      });
    },
    /**
     * @param {HTMLElement} element
     */
    leave(element) {
      requestAnimationFrame(() => {
        requestAnimationFrame(() => {
          element.style.height = '0px';
        });
      });
    },
    /**
     * @param {HTMLElement} element
     */
    afterLeave(element) {
      element.style.height = null;
    },
  },
});

new Vue({
  el: '#app',
  data: () => ({
    isOpen: true,
  }),
});

.enter-active,
.leave-active {
  overflow: hidden;
  transition: height .5s linear;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>

<div id="app">
  <button @click="isOpen = !isOpen">
    is open: {{ isOpen }}
  </button>
  <transition-collapse-height>
    <div v-show="isOpen">
      <div>1</div>
      <div>2</div>
      <div>3</div>
    </div>
  </transition-collapse-height>
</div>