<script>
var that = null;
export default {
  data () {
    return {
      setData: function (key,value) {
        that[key] = value
      }
    }
  },
}
<script>

  mounted () {
    that = this;
  },

step2： 

B页面js

1     getBrand (brand) {
2       let { from } = this.$root.$mp.query
3       let pages = getCurrentPages()
4       let page = pages.find( item => item.route.indexOf(from) != -1)
5       page.data.$root[0].setData('brand',brand)
6       wx.navigateBack({
7         delta: 1
8       });
9     }

讲解完毕，88， 下次见