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My question is as follows : In most or all tutorials that I read about closures their first and foremost asset is described as them being able to define private members . For example , from the fabulous nettuts website : http://net.tutsplus.com/tutorials/javascript-ajax/digging-into-design-patterns-in-javascript/ . My question is as follows - Why would you choose to create objects with closures , with their somewhat unnatural syntax , when you can use Object.definteProperty ? e.g 

var o = {}; // Creates a new object

 // Example of an object property added with defineProperty with a data property descriptor
Object.defineProperty(o, "a", {value : 37,
                           writable : false,
                           enumerable : true,
                           configurable : true});
 // 'a' property exists in the o object and its value is 37

I must admit both ways are much longer than traditional OOP languages , but isn't the second way more natural ? Why then are closures so popular , what other assets do they have and what is the difference between creating an object with a closure or with the way I just described?

Joel Blum
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2 Answers2

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Object.defineProperty still defines public properties, while closures allow privacy (you should not talk of private "members", it's just local variables).

Your example, using defineProperty to define a enumerable, writable and configurable data property can (and should) be abbreviated by the default property assignment (which works in older browsers as well):

o.a = 37;

Not all objects need to be created with closures (and in your example I can't think of any application), but you might want to learn How do JavaScript closures work?.

Community
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Bergi
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It is a matter of syntax preference and browser compatibility. One big gotcha, is if you want browser compatible code, the defineProperty method is only available in IE 9+ for non-dom objects.

As far as syntax goes, you can see that you loose a bit of what I call "visual encapsulation" when using defineProperty.

Each way has its own benefits, but both lack the simplicity of a language which supports privacy more directly.

Note:

  • I am assuming by priavate you mean you are setting the writable property to false.

Reference