vant-weapp/packages/collapse/index.ts

import { VantComponent } from '../common/component';

VantComponent({
  relation: {
    name: 'collapse-item',
    type: 'descendant',
    linked(child: Weapp.Component) {
      this.setData({
        items: [...this.data.items, child]
      }, () => {
        child.updateExpanded();
      });
    }
  },

  props: {
    accordion: Boolean,
    value: null
  },

  data: {
    items: []
  },

  watch: {
    value() {
      this.data.items.forEach(child => {
        child.updateExpanded();
      });
    },
    accordion() {
      this.data.items.forEach(child => {
        child.updateExpanded();
      });
    }
  },

  methods: {
    switch(name, expanded) {
      const { accordion, value } = this.data;
      if (!accordion) {
        name = expanded
          ? value.concat(name)
          : value.filter(activeName => activeName !== name);
      } else {
        name = expanded ? name : '';
      }
      this.$emit('change', name);
      this.$emit('input', name);
    }
  }
});