Design Patterns

38
CHAPTER 3 ■ ENCAPSULATION AND INFORMATION HIDING
// Privileged static method.
this.getUPPER_BOUND() {
return UPPER_BOUND;
}
...
// Return the constructor.
return function(constructorArgument) {
...
}
})();
If you have a lot of constants and don’t want to create an accessor method for each, you
can create a single generic accessor method:
var Class = (function() {
// Private static attributes.
var constants = {
UPPER_BOUND: 100,
LOWER_BOUND: -100
}
// Privileged static method.
this.getConstant(name) {
return constants[name];
}
...
// Return the constructor.
return function(constructorArgument) {
...
}
})();
Then you would get a constant by calling the single accessor:
Class.getConstant('UPPER_BOUND');
Singletons and Object Factories
There are other patterns that utilize closures to create a protected variable space. The two that
rely on it the most are the singleton pattern and the factory pattern. Both are covered in more
detail later in the book, but we mention them here because they use these same concepts to
hide information.
The singleton pattern uses a returned object literal to expose privileged members, while
keeping private members protected in the enclosing function’s scope. It uses the same technique
that we covered earlier, where an outer function is executed immediately and the result