Closures

It is when a local variable from inside a method can be used outside of the method itself.

Accesing bound values after closure
 

function warningMaker(obstacle) {
  return function(number, location) {
    alert("Beware! There have been " + obstacle +
          " sightings in the Cove today!\n" +
          number + " have been spotted at the " +
          location + "!");
  };
}

var killerPenguinAlert = warningMaker("killer penguin");

var snowYetiAlert      = warningMaker("snow yeti");

// call the two functions here

killerPenguinAlert(6, "Ice Caves");   // Beware! There have been killer penguin sightings in the Cove today! 6 have been spotted at the Ice Caves

snowYetiAlert(1, "Blizzard Beach");   // Beware! There have been snow yeti sightings in the Cove today! 1 have been spotted at the Blizzard Beach

Modifying bound values after closure
 

This sample shows how we can increase a variable within a given function

function buildCoveTicketMaker (transport ) {
  var passengerNumber = 0 ;
  return function ( name ) {
                                            passengerNumber++;
                                            alert("Here is your transportation ticket via the "+transport+".\n"+"Welcome to the Cold Closure Cave, "+ name + "!"+" You are passenger #"+passengerNumber+".");
                                        };
}

var getSubmarineTicket = buildCoveTicketMaker("Submarine");
getSubmarineTicket("Mario");