javascript

Chapter 6: Object-Oriented Programming
(continued)
SubType.prototype = new SuperType();
//first call to SuperType()
SubType.prototype.sayAge = function(){
alert(this.age);
};
The highlighted lines of code indicate when SuperType constructor is executed. When this code is
executed, SubType.prototype ends up with two properties: name and colors . These are instance
properties for SuperType, but they are now on the SubType ’ s prototype. When the SubType constructor
is called, the SuperType constructor is also called, which creates instance properties name and colors
on the new object that mask the properties on the prototype. Figure 6 - 6 illustrates this process.
Initially
SubType
prototype
SubType Prototype
constructor
SubType.prototype new SuperType()
SubType
prototype
SuperType Prototype
constructor
SubType
prototype
SubType Prototype
__proto__
constructor
name (undefined)
colors (array)
var instance new SubType("Nicholas", 29)
SuperType
prototype
SuperType Prototype
constructor
SubType
prototype
instance
__proto__
name "Nicholas"
colors (array)
age 29
Figure 6 - 6
SubType Prototype
__proto__
constructor
name (undefined)
colors (array)
180