element-plus/packages/transition/collapse-transition/index.vue

<template>
  <transition v-on="on">
    <slot></slot>
  </transition>
</template>
<script lang='ts'>
import { addClass, removeClass } from '@element-plus/utils/dom'

export default {
  name: 'ElCollapseTransition',
  setup() {
    return {
      on: {
        beforeEnter(el) {
          addClass(el, 'collapse-transition')
          if (!el.dataset) el.dataset = {}

          el.dataset.oldPaddingTop = el.style.paddingTop
          el.dataset.oldPaddingBottom = el.style.paddingBottom

          el.style.height = '0'
          el.style.paddingTop = 0
          el.style.paddingBottom = 0
        },

        enter(el) {
          el.dataset.oldOverflow = el.style.overflow
          if (el.scrollHeight !== 0) {
            el.style.height = el.scrollHeight + 'px'
            el.style.paddingTop = el.dataset.oldPaddingTop
            el.style.paddingBottom = el.dataset.oldPaddingBottom
          } else {
            el.style.height = ''
            el.style.paddingTop = el.dataset.oldPaddingTop
            el.style.paddingBottom = el.dataset.oldPaddingBottom
          }

          el.style.overflow = 'hidden'
        },

        afterEnter(el) {
          // for safari: remove class then reset height is necessary
          removeClass(el, 'collapse-transition')
          el.style.height = ''
          el.style.overflow = el.dataset.oldOverflow
        },

        beforeLeave(el) {
          if (!el.dataset) el.dataset = {}
          el.dataset.oldPaddingTop = el.style.paddingTop
          el.dataset.oldPaddingBottom = el.style.paddingBottom
          el.dataset.oldOverflow = el.style.overflow

          el.style.height = el.scrollHeight + 'px'
          el.style.overflow = 'hidden'
        },

        leave(el) {
          if (el.scrollHeight !== 0) {
            // for safari: add class after set height, or it will jump to zero height suddenly, weired
            addClass(el, 'collapse-transition')
            el.style.height = 0
            el.style.paddingTop = 0
            el.style.paddingBottom = 0
          }
        },

        afterLeave(el) {
          removeClass(el, 'collapse-transition')
          el.style.height = ''
          el.style.overflow = el.dataset.oldOverflow
          el.style.paddingTop = el.dataset.oldPaddingTop
          el.style.paddingBottom = el.dataset.oldPaddingBottom
        },
      },
    }
  },
}
</script>