expand.js

    enumerableProto.expand = function(selector) {
        var parent = this;
        return enumerableCreate(function () {
            var current, q = [parent], innerEnumerator;
            return enumeratorCreate(
                function () {
                    while (true) {
                        if (!innerEnumerator) {
                            if (q.length === 0) {
                                return false;
                            }
                            innerEnumerator = q.shift().getEnumerator();
                        }
                        if (innerEnumerator.moveNext()) {
                            current = innerEnumerator.getCurrent();
                            q.push(selector(current));
                            return true;
                        } else {
                            innerEnumerator.dispose();
                            innerEnumerator = undefined;
                        }
                    }
                },
                function () { return current; },
                function () {
                    if (innerEnumerator) {
                        innerEnumerator.dispose();
                    }
                }
            );
        });
    };