@iebh/bootstrap-vue/src/components/collapse/helpers/bv-collapse.js

With more than 85 components, over 45 available plugins, several directives, and 1000+ icons, BootstrapVue provides one of the most comprehensive implementations of the Bootstrap v4 component and grid system available for Vue.js v2.6, complete with extens

// Generic collapse transion helper component
//
// Note:
//   Applies the classes `collapse`, `show` and `collapsing`
//   during the enter/leave transition phases only
//   Although it appears that Vue may be leaving the classes
//   in-place after the transition completes
import { Vue, mergeData } from '../../../vue'
import { NAME_COLLAPSE_HELPER } from '../../../constants/components'
import { PROP_TYPE_BOOLEAN } from '../../../constants/props'
import { getBCR, reflow, removeStyle, requestAF, setStyle } from '../../../utils/dom'
import { makeProp } from '../../../utils/props'

// --- Helper methods ---

// Transition event handler helpers
const onEnter = el => {
  setStyle(el, 'height', 0)
  // In a `requestAF()` for `appear` to work
  requestAF(() => {
    reflow(el)
    setStyle(el, 'height', `${el.scrollHeight}px`)
  })
}

const onAfterEnter = el => {
  removeStyle(el, 'height')
}

const onLeave = el => {
  setStyle(el, 'height', 'auto')
  setStyle(el, 'display', 'block')
  setStyle(el, 'height', `${getBCR(el).height}px`)
  reflow(el)
  setStyle(el, 'height', 0)
}

const onAfterLeave = el => {
  removeStyle(el, 'height')
}

// --- Constants ---

// Default transition props
// `appear` will use the enter classes
const TRANSITION_PROPS = {
  css: true,
  enterClass: '',
  enterActiveClass: 'collapsing',
  enterToClass: 'collapse show',
  leaveClass: 'collapse show',
  leaveActiveClass: 'collapsing',
  leaveToClass: 'collapse'
}

// Default transition handlers
// `appear` will use the enter handlers
const TRANSITION_HANDLERS = {
  enter: onEnter,
  afterEnter: onAfterEnter,
  leave: onLeave,
  afterLeave: onAfterLeave
}

// --- Main component ---

export const props = {
  // // If `true` (and `visible` is `true` on mount), animate initially visible
  appear: makeProp(PROP_TYPE_BOOLEAN, false)
}

// --- Main component ---

// @vue/component
export const BVCollapse = /*#__PURE__*/ Vue.extend({
  name: NAME_COLLAPSE_HELPER,
  functional: true,
  props,
  render(h, { props, data, children }) {
    return h(
      'transition',
      // We merge in the `appear` prop last
      mergeData(data, { props: TRANSITION_PROPS, on: TRANSITION_HANDLERS }, { props }),
      // Note: `<transition>` supports a single root element only
      children
    )
  }
})