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I am trying to wrap my head around the idea of classes, data visibility and closures (specifically in Javascript) and I am On the jQuery docs page for types, it mentions that closures are used to hide data: The pattern allows you to create objects with methods that operate on data that isn't visible to the outside—the very basis of object-oriented programming. The example: function create() { var counter = 0; return { increment: function() { counter++; }, print: function() { console.log(counter); } } } var c = create(); c.increment(); c.print(); // 1 By declaring the variable counter with the keyword var, it is already locally scoped inside the function/class definition. As far as I know and can tell, it isn't accessible from the outside to begin with. Am I missing something from a data visibility perspective. Second, is there an advantage to writing the class like above versus like below: function create() { var counter = 0; this.increment = function() { counter++; } this.print = function() { console.log(counter); } return this; } var c = create(); c.increment(); c.print(); // 1 As I understand it, these are more or less semantically the same thing - the first is just more "jQuery style". I am just wondering if there is an advantage or other nuance I don't fully appreciate from the first example. If I am correct, both examples create closures in that they are accessing data declared outside their own scope. http://docs.jquery.com/Types#Closures

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