What methods do you know to implement JavaScript encapsulation?

The only method I'm familiar with relies on function scope, where the local variables declared within a function are all private to that function. So if you implement an object with your methods, wrap that along with your variables inside an anonymous function which returns the object, and then assign a variable by invoking the function, you have instantiated an object with fully encapsulated data. The inner object is known as a closure.

Here's a simple example:

var capsule = function() {
    var data = 42;
    return {
        getData: function() {
            return data;
        },
        setData: function(val) {
            data = val;
        }
    };
}();

Now nothing prevents you from accessing something named "capsule.data", but that is not the inner data variable. The real one can only be accessed via capsule.getData() and capsule.setData(n).