微信小程序：计算属性和监听属性miniprogram-computed

npm install --save miniprogram-computed

const computedBehavior = require("miniprogram-computed").behavior;
Component({
  behaviors: [computedBehavior],
  data: {
    a: 1,
    b: 1,
  },
  computed: {
    sum(data) {
      // 注意： computed 函数中不能访问 this ，只有 data 对象可供访问
      // 这个函数的返回值会被设置到 this.data.sum 字段中
      return data.a + data.b;
    },
  },
  methods: {
    onTap() {
      this.setData({
        a: this.data.b,
        b: this.data.a + this.data.b,
      });
    },
  },
});

const computedBehavior = require("miniprogram-computed").behavior;
Component({
  behaviors: [computedBehavior],
  data: {
    a: 1,
    b: 1,
    sum: 2,
  },
  watch: {
    "a, b": function (a, b) {
      this.setData({
        sum: a + b,
      });
    },
  },
  methods: {
    onTap() {
      this.setData({
        a: this.data.b,
        b: this.data.a + this.data.b,
      });
    },
  },
});