[masfuerte]

JavaScript has supported real data hiding since the beginning using closures. You define your object in a function. The function's local variables act as the private members of the object. They are accessible to all the methods but completely inaccessible to consumers of the object.

[hackrmn]

I completely forgot about closures. Frankly, they're still my go-to method for encapsulation, in part because the Java-isation of JavaScript done with the private class members and the onslaught of the "Alan Kay's ideas meet Simula" OOP flavour, is relatively new and I am still unsure whether it's a critical thing to have in JavaScript.