CODEWITHSUNDEEP
javascript
Barrie Reader
Barrie Reader

Reputation: 10713

Private vs Public Javascript Functions

can someone please explain what the difference is between these two functions?

(function(Engine, $, undefined) { //hidden from scope
    //public function below
    Engine.Init = function() {
        console.log("IM PUBLIC");
    }

    //anonymous functions below
    function Login() {
        console.log("IM PRIVATE");
    }
})( window.Engine = window.Engine || {}, jQuery );

Specifically, I'd like to know why Engine.Init() is available in the Console but Login isn't.

Upvotes: 4

Views: 334

Answers (4)

SLaks
SLaks

Reputation: 887469

Init is a property of the Engine object that refers to a function.
You can access it like any other property.

Login is a local variable within the anonymous, "immediately invoked function expression" (IIFE); like other local variables, its name is only visible within the declaring function

Upvotes: 7

Felix Kling
Felix Kling

Reputation: 816482

There is not really a difference between the functions themselves. The only difference is that the first function is assigned to a property of an object (Engine.init) defined in global scope (window.Engine), whereas the second function is defined locally inside the immediately invoked function expression (IIFE).

Here is a equivalent, but simpler example:

function foo() {
    // 1
    window.globalFunc = function() {
        // global/public
    }

    // 2
    function localFunc() {
        // local/private
    }
}

foo();

Because the first function is explicitly assigned to a global variable, it can be accessed outside of foo, after foo was executed. localFunc is not exported and hence local to foo, i.e. it cannot be accessed and doesn't exist outside of foo.

Upvotes: 2

Krasimir
Krasimir

Reputation: 13529

This thing

function(Engine, $, undefined) {
...
}

is actually a closure. So everything define inside that function is available only in that scope. When you do 

Engine.Init = ...

You create a property which is attached to Engine object. In your case Engine is a global object, which means that you have an access to it via the console.

Upvotes: 0

Michael Benin
Michael Benin

Reputation: 4332

Engine is global because of the parameters:

(window.Engine = window.Engine || {}, jQuery)

and available in the global namespace, if you did:

Engine.Login = function(){}

That would be available globally.

The function Login is only available inside the scope of the anonymous self executing function.

Upvotes: 2

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