prototype與__proto__區別

Each constructor is a function that has a property named “prototype” that is used to implement prototype-based inheritance and shared properties. Every object created by a constructor has an implicit reference (called the object's prototype) to the value of its constructor's “prototype” property.
When a constructor creates an object, that object implicitly references the constructor's prototype property for the purpose of resolving property references. The constructor's prototype property can be referenced by the program expression constructor.prototype, and properties added to an object's prototype are shared, through inheritance, by all objects sharing the prototype. Alternatively, a new object may be created with an explicitly specified prototype by using the Object.create built-in function. –ECMAScript® 2015 Language Specification

__proto__是每個對象都有的一個屬性，而prototype是函數才會有的屬性!!!

使用Object.getPrototypeOf()代替__proto__!!!

一、prototype

幾乎所有的函數（除了一些內建函數）都有一個名為prototype（原型）的屬性，這個屬性是一個指針，指向一個對象，而這個對象的用途是包含可以有特定類型的所有實例共享的屬性和方法。prototype是通過調用構造函數而創建的那個對象實例的原型對象。hasOwnProperty()判斷指定屬性是否為自有屬性；in操作符對原型屬性和自有屬性都返回true。

示例：自有屬性&原型屬性

var obj = {a: 1};
obj.hasOwnProperty("a"); // true
obj.hasOwnProperty("toString"); // false
"a" in obj; // true
"toString" in obj; // true

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