This is an example of a closure for self-study

closure.js

 // Closures will blow your mind or make you pull your hair out!

// One of the most difficult topics is that of closures.
// So I will write a small function that returns a function
// that calculates how many years we have left to retirement.

// retirementAge passes the age someone has to have
// in order to retire
function retirement(retirementAge) {
  var a = ' years left until retirement.';
  // although execution function finished
  // still able to use this variable even though
  // execution stopped
  return function(yearOfBirth) {
    var age = 2017 - yearOfBirth;
    console.log((retirementAge - age) + a);
  }
}
// log to console
// storing the above function in this variable
// which then declares the a variable
// then the execution context finishes
var retirementUS = retirement(67);
retirementUS(1990);

// alternate way to log this
retirement(67)(1990);

// CLOSURES SUMMARY
// An inner function always has access to the variables and parameters of its outer
// function, even after the outer function has returned.