JavaScript: Functional Programming for JavaScript Developers

Private variables

Closures are frequently used to encapsulate some information as private variables. JavaScript does not allow such encapsulation found in programming languages such as Java or C++, but by using closures, we can achieve similar encapsulation:

function privateTest(){
  var points=0;
  this.getPoints=function(){
    return points;
  };
  this.score=function(){
    points++;
  };
}

var private = new privateTest();
private.score();
console.log(private.points); // undefined
console.log(private.getPoints());

In the preceding example, we are creating a function that we intend to call as a constructor. In this privateTest() function, we are creating a var points=0 variable as a function-scoped variable. This variable is available only in privateTest(). Additionally, ...