Immediately Invoked Function Expression

Creating functions:

3 Ways to create a function in JS (Not ES6 or Json notation syntax):

Please see ES6 section to learn about other ways.

Function Statements and Function Expressions

Expressions: 
 - Unit of code that results in a value - Does not have to save to a variable

 Example:
     var a;
     a = 3 , returns 3 
     1 + 2 , returns 3

 Statements:
     - if(a === 3){}, we put an Expressions inside

Function Statements:
 - Does not return a value 
    function greet(){
        console.log("Hi")
    }

Function Expressions:
 - var anonymousGreet = function () {
     console.log("hi");
 }
 - It is an anonymous function, we call it by anonymousGreet()
 - Results in an new function object, so it is an Expressions

Function declaration

function example() {
  console.log("b");
}

Function expression

var example = function() {
  console.log(b);
}

Can think of that syntax as 2 parts.

Named function expression

var foo = function bar() { 
  console.log("b");
}
foo();
bar(); // Will result in Reference Error, cannot reference it by its name. 
       //Its only accessible within the function itself, like recursion.

Encapsulation using new scope

function exampleWrapper(){
   function private() {
     console.log("I am private"); -> This function is private
   }
   private();
}
exampleWrapper(); 
private(); -> Will not work as its private

//How to expose a function: 

function exampleWrapper(){
   var i = 10; 
   function private() {
     console.log("I am private"); -> This function is private
   }
   window.public = function() { -> Attaching it to the global scope 
     private() -> Still have access to private function 
     console.log("I am public + "i is" + i++); 
   }
}
exampleWrapper(); 

//But their is a problem:

This wrapper function exampleWrapper() has a name and is public. 
 - Invoking public() -> results in "I am public i is 16" 
 - Invoking public() -> results in "I am public i is 17" 
 - Invoking exampleWrapper() results in undefined. (We should not be able to do but we can..) 
 - then invoking public() -> results in "I am public i is 10" (Not 18, whyy?) 
 - Whats happening is when we invoke exampleWrapper() a new block of memory is allocated, so variable "i" is initialise again. 

//How to solve that? We need to create an IFFE, so the function does not have a name.