closure.js

// closure is a function having access to the parent 
// scope
function greet() {
    var message = "Good evening";

    function sayHi() {
        console.log(message);
    } // Here closure is created, 
    // sayHi function has access to message variable

    return sayHi;
} // greet function is returning another function named sayHi
// sayHi is a function declared inside greet function

var fn = greet(); // returns sayHi function
fn(); // sayHi function is called

console.log(message); // message is not accessible here
// because message is not in the global scope
// the reason it is not in the global scope is because
// greet function has returned and it's execution context
// has been removed from the stack

// message here is also the private variable
// we call it as a private variable because it is not
// accessible outside the greet function