如何將新屬性及其參數添加到現有原型/構造函數中

Question

這僅用於教育目的，比如我有一個現有的原型/構造函數：

var Dog = function(name, age, color){
this.name = name;
this.age = age;
this.color = color;
};

var pitBull = new Dog('Rocky', 5, 'black');

我想添加（通過編碼）一個名為type的新參數，如下所示：

    var Dog = function(name, age, color, type){
    // code goes here.. };

同時我想添加一個具有確切名稱的新屬性，如下所示：

    this.type = type;

所以我可以這樣做：

    var pitBull = new Dog('Rocky', 5, 'black', 'PitBull');

有任何想法嗎？

Answer 1

首先，讓我們澄清原型與構造函數不同。 你展示的是一個構造函數。 此函數將用於構造符合您創建的接口的新對象，但它也將繼承底層對象的屬性 - 該對象是原型。

// This is your constructor function that takes arguments that help
// it construct the instance properties:
var Dog = function(name, age, color){
  // These are the instance properties
  this.name = name;
  this.age = age;
  this.color = color;
};

// And, here you are constructing a new instance of Dog
var pitBull = new Dog('Rocky', 5, 'black');

“我想添加（通過編碼）一個名為type的新參數，就像這樣”

var Dog = function(name, age, color, type){
// code goes here.. };

在構造器的基本參數結構制作完成后，更改構造函數的基本參數結構確實不是正確的方法。 您應該做的是使用新的構造函數創建一個新的子類型，並使新類型繼承舊類型。 新類型將采用所有4個參數，但它只會設置最新的參數，它會將其他3個參數傳遞給它繼承的基礎對象。

“同時我想添加一個具有確切名稱的新屬性”

沒問題：

// Make new constructor function
function BetterDog(name, age, color, type){
  this.type = type;  // New property based on new parameter value

  // Now pass the original 3 parameters to the prototype
  // and let that object will handle the arguments as normal
  Dog.prototype.constructor.call(this, name, age, color);
}

// Now, we'll set this new object to inherit from the earlier one by setting
// it's prototype to a new instance of a Dog. A new BetterDog is now going
// to inherit all the properties of Dog
BetterDog.prototype = new Dog();

// But, one problem here is that when we try to make a new instance of 
// BetterDog, the Dog constructor function will be called. This happens
// because we switched the prototype. We can fix that like this:
BetterDog.constructor = BetterDog;

// Finally, we can construct a new BetterDog with all 4 parameters:
var pitBull = new BetterDog('Rocky', 5, 'black', 'PitBull');

整個事情在一起：

  // This is your constructor function that takes arguments that help // it construct the instance properties: var Dog = function(name, age, color){ // These are the instance properties this.name = name; this.age = age; this.color = color; }; // Make new constructor function function BetterDog(name, age, color, type){ this.type = type; // Now pass the original 3 parameters to the prototype // and let that object will handle the arguments as normal Dog.prototype.constructor.call(this, name, age, color); } // Now, we'll set this new object to inherit from the earlier one by setting // it's prototype to a new instance of a Dog. A new BetterDog is now going // to inherit all the properties of Dog BetterDog.prototype = new Dog(); // But, one problem here is that when we try to make a new instance of // BetterDog, the Dog constructor function will be called. This happens // because we switched the prototype. We can fix that like this: BetterDog.constructor = BetterDog; // Finally, we can construct a new BetterDog with all 4 parameters: var pitBull = new BetterDog('Rocky', 5, 'black', 'PitBull'); // Test: console.log(pitBull.name); console.log(pitBull.age); console.log(pitBull.color); console.log(pitBull.type);