Closure Example

gistfile1.txt

You can think of clousre as a way of "remember" and continue to access a function's scope even once the function has finished running.

function makeAddr(x)
{
  //paraneter 'x' is an inner variable
  
  //inner function add() uses 'x', so it has clousre over it
  function add(y)
  {
    return x + y;
  }
  return add;
}

var plusOne = makeAddr(1); 

plusOne(10); // it will return 11 as it remembers the value of outerscope x 

var plusTen = makeAddr(10);

plusTen(10); // it will return 20 as it remembers the value of outerscope which is 10;

steps on how code works
1) when we call makeAddr(1), we get back a rederence to its inner add(...) that remembers x as 1. 
we call this function reference plusOne(...).

2) when we call plusOne(3), it adds 3(its inner y)to the 1(remembered by x), and we get 4 as the result.'

Modules
// the most common usage of closure in Javascript is the module pattern.

// modules let you define private implementation details (variables, function) that are hidden from the outside world, as well as a public API that is accesible from the outside.