Javascript prototype and class access problems

Question

Family = function(name) { this._Name = name; } Family.prototype = { getName: function() { return this._Name; }, People: function(num) { this._Number = num; } } Family.People.prototype = { clearNumber: function() { this._Number = 0; } } 

People are a nested class. His parent class is Family.

I get a Family.People undefined error message. Can someone fix the code above?

Answer 1

Working code

 // function doesn't need "new" operator var Family = function(name) { this._Name = name; }; Family.prototype = { getName: function() { return this._Name; }, // missing comma People: function(num) { this._Number = num; } }; // work with prototypes Family.prototype.People.prototype = { clearNumber: function() { this._Number = 0; } }; 

That will work. But you should know that when you call:

 var f = new Family("Doe"); 

f.People is just an object constructor, not an instance of any other object. You will need to create an instance as well:

 f.members = new f.People(3); 

You have a constructor inside your instance that is pretty confusing.

Best approach

Thus, it would be better if you pressed your prototypes as follows:

 var Family = function(name) { this._Name = name; this.getName = function() { return this._Name; }; }; Family.People = function(num) { this._Number = num; this.clearNumber = function() { this._Number = 0; }; }; 

This actually makes the class inside the class (and not inside the instances). Thus, the top lines will be called as follows:

 var f = new Family("Doe"); f.members = new Family.People(3); 

The scan for instance f will look like this:

 f _Name getName() members _Number clearNumber() 

Private variables

 var Family = function(name) { var _name = name; this.getName = function() { return _name; }; }; Family.People = function(num) { var _num = num; this.getNumber = function() { return _num; } this.clearNumber = function() { _num = 0; }; }; 

Thus, we make variables private and accessible only internally, so they cannot be manipulated externally. You should always use functions to control them. This makes it more reliable, especially when there are certain business rules related to variable values.

 var f = new Family("Doe"); f._name; // this is undefined because "_name" is private closure variable 

The sweep of an instance of f will now look more like an instance of a class object:

 f getName() members getNumber() clearNumber() 

Answer 2

Note that you assign Family.prototype.People , then try to access Family.People .

Family not an instance of Family , so it does not have the properties of this class - Family is an instance of Function , so you are trying to access Function.prototype.People in this third expression. (this makes it a little easier)

i.e. what do you want to do is

 Family.prototype.People.prototype = { clearNumber:function(){this._Number = 0;} } 

You also lack a comma in front of people, but I guess this is a typo ...

Answer 3

You must declare the People constructor as the key in the Family object:

 Family.People = function(num) { this._Number = num; } 

The family prototype will be in the prototype chain for new Family objects; and not part of the Family itself.