functions.js

// Functions are 'first-class' objects.
var myFunction = function(){
  console.log("I have been called.");
}
myFunction.firstName = 'Manoj'; // we can attach attributes to functions because they are also objects.
console.log(myFunction);

// Functions can be anonymous.
setTimeout(function(){
  console.log("hello, i have been called after 1 second.")
},1000);

// Function can be self executing.
(function(){
  console.log("I have been called immediately.")
})(); 

// Encapsulation in JavaScript.
(function(){
  var message = "hello world.";
})();

if(typeof message === 'undefined'){
  console.log('I cannot access the value of message.')
} /* this demonstrates encapsulation in Javascript. Variables defined in the self executing function above 
   * cannot be accessed from outside. That function has it's own scope. */
   
// Functinos encapsulate and capture scope. 
(function(){
  var messages = ['hello', 'world'];
  for (var i in messages){
    setTimeout(function(){
      console.log(messages[i]);
    }, 10);
  }
})(); // Result: world, world. gotcha! 
      // (setTimeout is called inside the scope of 'for' block. The value of i inside the 'for' block is passed to SetTimeout.)

(function(){
  var messages = ['hello', 'world'];
  for (var i in messages){
    setTimeout((function(myVal){
      console.log(messages[myVal]);
    })(i), 10);
  }
})(); // Result: hello, world. (We are now passing value of i in each iteration to the function as a local parameter myVal. 
      // Each time its separate scope and keep it's myVal values separately. )