ES6_Assign at once.js

class Test {
  constructor() {
    this.data = {
      name: null,
      age: -1,
      attr: null
    }
  }
  init() {
    this.data = {
      name: 'Alice',
      age: 5,
      attr: this.data.name + ' is ' + this.data.age + ' year old.'
    }
  }
}

a.init()
//  undefined
a.data.attr
//  "null is -1 year old."