對象未定義與Knockout數據映射插件

Question

我試圖使用映射插件，使兒童對象的屬性可觀察。我有以下幾點：

// setData defined here 

var mapping = { 

    create: function(options) { 
     //customize at the root level. 
     var innerModel = ko.mapping.fromJS(options.data); 
     innerModel.cardCount = ko.computed(function() { 
      debugger; 
      return this.cards().length; // cards not defined - "this" is Window for some reason 
     }); 

     innerModel.deleteCard = function (card) { 
      // Pending UI 
      // call API here 
      // On success, complete 
      this.cards.remove(card); 
     }.bind(this); 

     innerModel.addCard = function() { 
      //debugger; 
      // Pending UI 
      // Call API here 
      // On success, complete 
      this.cards.push(dummyCard); 
      //this.cardToAdd(""); 
     }.bind(this); 

     return innerModel; 
    } 
}; 

var SetViewModel = ko.mapping.fromJS(setData, mapping); 

ko.applyBindings(SetViewModel); 

當我在Chrome調試器中運行，我得到「對象[對象全局]有沒有方法卡」。卡應是一個可觀察的數組。我究竟做錯了什麼？

Answer 1

innerModel.cardCount = ko.computed(function() { 
      debugger; 
      return this.cards().length; // cards not defined - "this" is Window for some reason 
     }); 

this是你創建，並因此被綁定到全局對象匿名函數內部。如果你想引用innermodel，你必須直接這樣做，或者將innermodel綁定到函數。

innerModel.cardCount = ko.computed(function() { 
      return innerModel.cards().length; 
     }); 

或

var computedFunction = function() { 
      return this.cards().length; 
     }; 
innerModel.cardCount = ko.computed(computedFunction.apply(innerModel));