[Vue Reactive Data] How to implement a Vue styled reactive data.

index.js

// 元数据
let a = { 
  source: { number: 0 }
}

// 核心：Object.defineProperty
Object.defineProperty(a, 'number', {
  enumerable: true, 
  configurable: true, 
  get: function () { 
    return this.source.number 
  }, 
  set: function (val) { 
    console.log(this.source.number, '-->', val); 
    this.source.number = val 
  } 
})