Q:

Javascript Prototype not Working

Hi I don't know whether this is my mistake in understanding Javascript prototype object .. 
Well to be clear I'm new to the Javascript singleton concept and lack clear cut knowledge in that but going through some referral sites I made a sample code for my system but it's giving out some errors which I couldn't find why so I'm asking for your help. My code is:
referrelSystem = function(){
//Some code here
}();

Prototype function:
referrelSystem.prototype.postToFb = function(){
//Some Code here
};

I get an error saying prototype is undefined!
Excuse me i thought of this right now 
EDIT
I have used like this: 
referrelSystem = function(){
 return{
        login:getSignedIn,
        initTwitter:initTw
    }
};

Is this causing an issue?

A:

A typical way to define a JavaScript class with prototypes would be:
function ReferrelSystem() {
    // this is your constructor
    // use this.foo = bar to assign properties
}

ReferrelSystem.prototype.postToFb = function () {
    // this is a class method
};

You might have been confused with the self-executing function syntax (closures). That is used when you would like to have "private" members in your class. Anything you declare in this closure will only be visible within the closure itself:
var ReferrelSystem = (function () {
    function doSomething() {
        // this is a "private" function
        // make sure you call it with doSomething.call(this)
        // to be able to access class members
    }

    var cnt; // this is a "private" property

    function RS() {
        // this is your constructor
    }

    RS.prototype.postToFb = function () {
        // this is a class method
    };

    return RS;
})();

I would recommend that you study common module patterns if you're looking into creating a library.

A:

I don't think you intend to immediately execute the functions, change them to this:
var referrelSystem = function(){
//Some code here
};

(+var, -())
Same with the prototype function:
referrelSystem.prototype.postToFb = function(){
//Some Code here
};

(Here you don't need the var, because you're assigning to something that already exists.)

A:

Update: Seeing your updated code, the return from referrelSystem won't work as expected, since return values are discarded when calling new referrelSystem().
Rather than returning an object, set those properties to this (the instance of referrelSystem that gets constructed):
var referrelSystem = function () {
    // I assume you have other code here

    this.login = getSignedIn;
    this.initTwitter = initTw;
};

