How to Create Protected Object Properties in JavaScript

Question

Is there a JavaScript pattern which mimics \"Protected\" object properties like what you see in languages like C++ ??

Basically, I\'d like to create an Object A whic

Answer 1

Take a look at workaround proposed by Maks on his website: Emulating protected members in JavaScript

It emulates protected access level to methods and properties of an object.

Answer 2

I found a way for creating protected members. Therefor I call the base constructor and return an object with the protected members at the same time:

var protected = BaseClass.call(this); 

Here an example:

function SignedIntegerArray(size)
{
    var public = this;
    var protected = {};

    // private property:
    var _maxSize = 10000;
    // protected property:
    protected.array = [];
    // public property:
    public.Length = size;

    if(!isInteger(size) || size < 0 || size > _maxSize) { throw "argument exception"; }
    for(var index = 0; index != size; index++) { protected.array[index] = 0; }

    // private method:
    function isInteger(i) { return i == i + 0 && i == ~~i; }
    // protected method:
    protected.checkIndex = function(index) { return index >= 0 && index < size; }
    // public methods:
    public.SetValue = function(index, value) { if(protected.checkIndex(index) && isInteger(value)) { protected.array[index] = value; } };
    public.GetValue = function(index) { if(protected.checkIndex(index)) { return protected.array[index]; } else { throw "index out of range exception"; }}

    return protected;
}

function FloatArray(size, range)
{
    var public = this;
    var protected = SignedIntegerArray.call(this, size); // call the base constructor and get the protected members 

    // new private method, "isInteger" is hidden...
    function isFloat(argument) { return argument != ~~argument; }
    // ...but "checkIndex" is accessible
    public.SetValue = function(index, value) { if(protected.checkIndex(index) && isFloat(value) && value >= public.MinValue && value <= public.MaxValue) { protected.array[index] = value; } };

    // new public properties:
    public.MinValue = -range;
    public.MaxValue = range;

    return protected; // for sub-classes
}

function newObject(className, args) { return new function() { className.apply(this, args)}} // you need to use function.call or function.apply to initialize an object. otherwise the protected-object is empty.
window.addEventListener("load", function()
{
    var o = newObject(FloatArray, [4, 50.0]);
    o.SetValue(3, 2.1);
    console.log(o.GetValue(3));
    console.log(o.Length); // property from the base-class
});