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I like the module pattern that returns constructors as described in: http://elegantcode.com/2011/02/15/basic-javascript-part-10-the-module-pattern/

However I am not sure how to inherit from an object that is implemented with this pattern. Suppose I have a parent object implemented thus...

namespace('MINE');  

MINE.parent = (function() { 
    // private funcs and vars here

    // Public API - constructor
    var Parent = function (coords) {
       // ...do constructor stuff here
    };

    // Public API - prototype
    Parent.prototype = {
       constructor: Parent,
       func1:  function ()    { ... },
       func2:  function ()    { ... }
    }

    return Parent;
 }());

How do I define a child object that also uses the module pattern that inherits from parent in such a way that I can selectively override, for example, func2?

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2
  • Just a note, the code you've provided has a bug -- you're setting the constructor to undefined. I've edited to fix it. Commented Jun 18, 2012 at 17:51
  • I just asked a similar question here stackoverflow.com/questions/16659326/… - wondering what you think of it. Commented May 21, 2013 at 18:33

2 Answers 2

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20 
MINE.child = (function () {

  var Child = function (coords) {
    Parent.call(this, arguments);    
  }

  Child.prototype = Object.create(Parent.prototype);

  Child.prototype.constructor = Child;
  Child.prototype.func2 = function () { ... };

  return Child;

}());
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7 Comments

Thank you. This was a very terse and clear answer and worked fine for me. I do like this pattern because it encompasses one-time initialization, encapsulation and with your code above, inheritance. Do you see any major pitfalls to the pattern?
@AndrewS. I personally hate namespaces. But that's a style preference. You can use module loaders instead.
This isn't working for me. If I were to instantiate a MINE.child, I can't access func1 (as defined in MINE.parent). Am I missing something?? And is the child's func2 supposed to replace the parent's func2?
The problem with this approach is that you can have an equivalent of static variable, but not private variable. I'm still looking for a better way.
@juminoz the only non-horrendously-hacky way I know of doing private instance variables is to define them in the constructor and define all methods that rely on them in the constructor too, with this.method = . Unfortunately I strongly dislike this way of doing things, as it creates a new function object for every instance rather than reusing the one on the prototype. I tend to avoid using private instance variables for that reason.
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I find the solution from this blog (http://metaduck.com/08-module-pattern-inheritance.html) cleaner. For example:

function Parent(name) {
    // Private variables here
    var myName;

    // Constructor
    myName = name;

    // Public interface
    return {
        func1: function () {alert("Parent func1. Name: " + myName); },
        func2: function () {alert("Parent func2. Name: " + myName); }
    }
}

function Child(name) {
    // Private variables here
    var myName,
        exportObj;

    // Constructor
    // Inherit
    exportObj = Parent(name + "'s father");

    // Override
    exportObj.func2 = function () {
        alert("Child func2. Name: " + name);
    }

    // Export public interface
    return exportObj;
}

An example can be run here: http://jsfiddle.net/wt4wcuLc/

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