Private members when extending a class using ExtJS

Question

I have done some research on the ExtJS forum regarding private methods and fields inside a extended class, and I couldn't find any real answer to this.

And when I say an extended class I mean something like this:

Ext.ux.MyExtendedClass = Ext.extend(Ext.util.Observable, {
    publicVar1: 'Variable visible from outside this class',
    constructor: function(config) { this.addEvents("fired"); this.listeners = config.listeners; }, // to show that I need to use the base class
    publicMethod1: function() { return 'Method which can be called form everywhere'; },
    publicMethod2: function() { return this.publicMethod1() + ' and ' + this.publicVar1; } // to show how to access the members from inside another member
});

The problem here is that everything is public. So, how do I add a new variable o method within the scope of MyExtendedClass that cannot be accessed from outside but can be access by the public methods?

Answer 1

The following example shows the Upper Stage way to define privileged private & public members. But it also shows how to define private static members (also called class members), and public non-privileged members. Using these last 2 instead of the privileged ones, we will reduce initialization time as they are not parsed every time you create a new object of your class:

Ext.ux.MyExtendedClass = Ext.extend(Ext.util.Observable, 
  (function() {
    // private static fields (can access only to scope: minimum privileges).
    var privStaticVar = 0;
    // private static functions (can access only to scope and arguments, but we can send them the scope by param)
    var privateFunc1 = function(me) { return me.name + ' -> ClassVar:' + privStaticVar; };
    var privateFunc2 = function(me) { return me.publicMethod1() + ' InstanceVar:' + me.getPrivateVar(); };
    return {
      constructor: function(config) {
        // privileged private/public members (can access to anything private and public)
        var privateVar = config.v || 0;
        var privInstFunc = function() { privateVar += 1; };
        this.name = config.name;
        this.incVariables = function(){ privInstFunc(); privStaticVar += 1; };
        this.getPrivateVar = function(){ return privateVar; };
      },
      // public members (can access to public and private static, but not to the members defined in the constructor)
      publicMethod1: function() { this.incVariables(); return privateFunc1(this); },
      publicMethod2: function() { return privateFunc2(this); }
    };
  }())
);

function test() {
  var o1 = new Ext.ux.MyExtendedClass({name: 'o1', v: 0});
  var o2 = new Ext.ux.MyExtendedClass({name: 'o2', v: 10});
  var s = o1.publicMethod2() + '<br>' + o1.publicMethod2() + '<br><br>' + o2.publicMethod2() + '<br>' + o2.publicMethod2();
  Ext.get("output").update(s);
}

<link href="//cdnjs.cloudflare.com/ajax/libs/extjs/3.4.1-1/resources/css/ext-all.css" rel="stylesheet"/>
<script src="//cdnjs.cloudflare.com/ajax/libs/extjs/3.4.1-1/adapter/ext/ext-base.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/extjs/3.4.1-1/ext-all.js"></script>

<p>Click the button to instantiate 2 objects and call each object 2 times:</p>

<button onclick="test();">Test</button>

<p>You can click the button again to repeat. You'll see that the static variable keep increasing its value.</p>

<p>&nbsp;</p>
<div id="output"></div>