javascript

Chapter 6: Object-Oriented Programming
Object
prototype
Object Prototype
constructor
hasOwnProperty
isPrototypeOf
propertyIsEnumerable
toLocaleString
toString
valueOf
(function)
(function)
(function)
(function)
(function)
(function)
SuperType
prototype
SuperType Prototype
__proto__
constructor
getSuperValue (function)
SubType
prototype
instance
__proto__
subproperty false
Figure 6-5
SubType Prototype
__proto__
property
true
getSubValue (function)
SubType inherits from SuperType , and SuperType inherits from Object . When instance.
toString() is called, the method being called actually exists on Object.prototype .
Prototype and Instance Relationships
The relationship between prototypes and instances is discernable in two ways. The first way is to use the
instanceof operator, which returns true whenever an instance is used with a constructor that appears
in its prototype chain, as in this example:
alert(instance instanceof Object);
alert(instance instanceof SuperType);
alert(instance instanceof SubType);
//true
//true
//true
Here, the instance object is technically an instance of Object , SuperType , and SubType due to the
prototype chain relationship. The result is that instanceof returns true for all of these constructors.
The second way to determine this relationship is to use the isPrototypeOf() method. Each prototype
in the chain has access to this method, which returns true for an instance in the chain as in this example:
alert(Object.prototype.isPrototypeOf(instance)); //true
alert(SuperType.prototype.isPrototypeOf(instance)); //true
alert(SubType.prototype.isPrototypeOf(instance)); //true
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