element-plus/packages/components/collapse/src/collapse.vue

<template>
  <div class="el-collapse" role="tablist" aria-multiselectable="true">
    <slot></slot>
  </div>
</template>

<script lang="ts">
import { defineComponent, ref, watch, provide } from 'vue'
import { UPDATE_MODEL_EVENT, CHANGE_EVENT } from '@element-plus/utils/constants'
import type { PropType } from 'vue'
import type { CollapseProvider } from './collapse.type'

export default defineComponent({
  name: 'ElCollapse',
  props: {
    accordion: Boolean,
    modelValue: {
      type: [Array, String, Number] as PropType<
        string | number | Array<string | number>
      >,
      default: () => [],
    },
  },
  emits: [UPDATE_MODEL_EVENT, CHANGE_EVENT],
  setup(props, { emit }) {
    const activeNames = ref([].concat(props.modelValue))

    const setActiveNames = (_activeNames) => {
      activeNames.value = [].concat(_activeNames)
      const value = props.accordion ? activeNames.value[0] : activeNames.value
      emit(UPDATE_MODEL_EVENT, value)
      emit(CHANGE_EVENT, value)
    }

    const handleItemClick = (name) => {
      if (props.accordion) {
        setActiveNames(
          (activeNames.value[0] || activeNames.value[0] === 0) &&
            activeNames.value[0] === name
            ? ''
            : name
        )
      } else {
        const _activeNames = activeNames.value.slice(0)
        const index = _activeNames.indexOf(name)

        if (index > -1) {
          _activeNames.splice(index, 1)
        } else {
          _activeNames.push(name)
        }
        setActiveNames(_activeNames)
      }
    }

    watch(
      () => props.modelValue,
      () => {
        activeNames.value = [].concat(props.modelValue)
      }
    )

    provide<CollapseProvider>('collapse', {
      activeNames,
      handleItemClick,
    })

    return {
      activeNames,
      setActiveNames,
      handleItemClick,
    }
  },
})
</script>