如何使用Object.defineProperties？

Question

大家，我最近读了Professional.JavaScript.for.Web.Developers.3rd.Edition。这是我从中学到的代码。但是，输出与我读过的书有所不同。当我运行下面的代码时，ref.child("Enterpriser Listings").child("Sell Old Stuff - Listings").observe(.value, with: { (snapshot:FIRDataSnapshot) in var users = [User]() for child in snapshot.children { print("\((sweet as! FIRDataSnapshot).value)") if let dictionary = child.value as? [String : AnyObject] { let user = User() user.setValuesForKeys(dictionary) users.append(user) } } self.userList = users self.tableView.reloadData() }) ，book.edition is 1是2004而book._year是2004.会发生什么？我的代码出了什么问题？

book.year

Answer 1

对象的属性_year和edition应定义为可写。否则，在年度制定者中重新定义它们是没用的。

var book = {};

Object.defineProperties(book, {
  _year: {
    value: 2004,
    writable:true
  },
  edition: {
    value: 1,
    writable:true
  },

  year: {
    
    get: function() {
      return this._year;
    },

    set: function(newValue) {
      
      if (newValue > 2004) {
        this._year = newValue;
        this.edition += newValue - 2004;
      }
    }
  }
});


console.log(book.edition);
console.log(book.year);
book.year=2005;
console.log(book.edition);
console.log(book.year);