vant-weapp/packages/tabbar/index.ts

import { VantComponent } from '../common/component';
import { safeArea } from '../mixins/safe-area';

VantComponent({
  mixins: [safeArea()],

  relation: {
    name: 'tabbar-item',
    type: 'descendant',
    linked(target: Weapp.Component) {
      this.children = this.children || [];
      this.children.push(target);
      this.setActiveItem();
    },
    unlinked(target: Weapp.Component) {
      this.children = this.children || [];
      this.children = this.children.filter(item => item !== target);
      this.setActiveItem();
    }
  },

  props: {
    active: Number,
    activeColor: String,
    fixed: {
      type: Boolean,
      value: true
    },
    zIndex: {
      type: Number,
      value: 1
    }
  },

  watch: {
    active(active: number) {
      this.currentActive = active;
      this.setActiveItem();
    }
  },

  created() {
    this.currentActive = this.data.active;
  },

  methods: {
    setActiveItem(): Promise<any> {
      if (!Array.isArray(this.children) || !this.children.length) {
        return Promise.resolve();
      }
      return Promise.all(
        this.children.map((item: Weapp.Component, index: number) =>
          item.setActive({
            active: index === this.currentActive,
            color: this.data.activeColor
          })
        )
      );
    },

    onChange(child: Weapp.Component) {
      const active = (this.children || []).indexOf(child);

      if (active !== this.currentActive && active !== -1) {
        this.currentActive = active;
        this.setActiveItem().then(() => {
          this.$emit('change', active);
        });
      }
    }
  }
});