Confused about JavaScript prototypal inheritance...

Question

In the book "JavaScript the definitive guide 5 edition", section 9.2 Prototypes and Inheritance, I find the following words:

In the previous section, I showed that the new operator creates a new, empty object and then invokes a constructor function as a method of that object. This is not the complete story, however. After creating the empty object, new sets the prototype of that object. The prototype of an object is the value of the prototype property of its constructor function. All functions have a prototype property that is automatically created and initialized when the function is defined. The initial value of the prototype property is an object with a single property. This property is named constructor and refers back to the constructor function with which the prototype is associated. (You may recall the constructor property from Chapter 7 ; this is why every object has a constructor property.) Any properties you add to this prototype object will appear to be properties of objects initialized by the constructor.

Now, if that is true, how could prototypal inheritance exists? I mean, let's say the prototype object of a constructor function has a constructor property initially. Because the prototype object itself is an object, to determine its constructor we often use prototype_object.constructor. But now the prototype_object already has a constructor property itself, and it points to the constructor function with which the prototype is associated. In this situation how can inheritance exists?

Answer 1

If you have an object obj, it's prototype is obj.prototype and constructor property referring to obj's constructor is obj.prototype.constructor.

For the object obj.prototype the situation is the same. Let's say proto = obj.prototype, then the reference to the constructor of proto would be found at proto.prototype.constructor.

This is the same as obj.prototype.prototype.constructor, so there is no conflict with obj.prototype.constructor.

Answer 2

Don't worry about the constructor property - it is irrelevant. Skip those sentences and you might follow it better.

If you are still unsure of your understanding, google for __proto__ - the internal prototype reference on JS objects. It is even exposed to scripts on Firefox and Safari.

A good reference is https://developer.mozilla.org/en/Core_JavaScript_1.5_Guide/The_Employee_Example/Object_Properties/Inheriting_Properties