Javascript 对象创建

//JS里面创建一个对象最简单的方式是通过{}来直接建立
const bookLiteral = {
  bookName : 'Program',
  bookPrice : '30',
  calcPrice : function(){}
};

//如果需要建立同类型的对象，可以用工厂，或者构造器

//factory function
function createBook(bookName, bookPrice) {
  return {
    bookName,
    bookPrice,
    calcPrice :function (numOfBooks){
      return this.bookPrice * numOfBooks;
    }
  }
}

bookFromFactory = createBook("Factory Object", 15);
console.log(bookFromFactory);
console.log(bookFromFactory.calcPrice(30));

//constructor function
function Book(bookName, bookPrice){
  this.bookName = bookName;
  this.bookPrice = bookPrice;
  this.calcPrice = function (numOfBooks){
    return this.bookPrice * numOfBooks;
  }
}

//js里的new 实际上先生成一个object，然后在这个object上，通过this, 动态增加属性和方法
myBook = new Book('JS', 10);
console.log(myBook.constructor);

for (let key in myBook){
  console.log(key, myBook[key]);
}

const keys = Object.keys(myBook);
console.log(keys);

if ('bookPrice' in myBook) {
  console.log('the price of 10 books: ', myBook.calcPrice(10));
}else
  console.log('price of book:', myBook.calcPrice(1));


//js 的普通{} 都是对外直接访问的，这就导致无法真的做到oop，最起码的封装就没有
//所以需要通过曲线的方式来实现封装，比如：closur, getter , setter
function Circle(radius){
  this.radius = radius;
  //defaultLocation 外部是访问不到的，因为没有把这个defaultLocation加到this的属性上
  let defaultLocation = {x:10, y:10};
  this.draw = function (){
    console.log('DefaultLocation:', defaultLocation);//这里用到了closure backpack
  };
  //getter setter
  Object.defineProperty(this, 'defaultLocation', {
    get: function(){
      return defaultLocation;
    },
    set: function(value){
      if (!value.x || !value.y){
        throw new Error('Not Valid Value');
      }
      defaultLocation = value;
    }
  });
}

var circle = new Circle(10);
//circle.defaultLocation = {x:3};   不符合合法性校验
circle.defaultLocation = {x:3, y:5};
console.log(circle.defaultLocation);