id.js

/*======================================================================*\
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\*======================================================================*/

if (NAMESPACE == null
        || typeof (NAMESPACE) == 'undefined') {
    NAMESPACE = {};

    // Creates an object that allocates a new or references an
    // existing very expensive resource associated with `id`
    var resource = function (id) {
        // Private data
        var _all_ids = new Array();
        var _closed = false;
        var _id = id;
        var _expensive_resource = null;

        // Public data
        var persona = {
        };

        // Public methods
        var getExpensiveResource = function () {
            return _expensive_resource;
        }

        persona.getExpensiveResource = getExpensiveResource;

        var getId = function () {
            return _id;
        }

        persona.getId = getId;

        var close = function () {
            delete _all_ids[_id];
            this._closed = true;
        }

        persona.close = close;

        // Private methods
        function _lookupOrCreateExpensiveResourceById(id) {
            _expensive_resource = _all_ids[id];

            if (_expensive_resource == null) {
                // Just pretend for the sake of this example
                _expensive_resource = {
                    value: "I'm a very expensive resource associated with ID " + id
                };

                _all_ids[id] = _expensive_resource;
            }

            return _expensive_resource;
        }

        // Initialization
        _expensive_resource = _lookupOrCreateExpensiveResourceById(id);

        return persona;
    }

    NAMESPACE.resource = resource;
}