build/lib/tsb/utils.ts/Graph/_traverse
class Graph:        private _traverse(node: Node<T>, inwards: boolean, seen: { [key: string]: boolean }, callback: (data: T) => void): void {
            const key = this._hashFn(node.data);
            if (collections.contains(seen, key)) {
                return;
            }
            seen[key] = true;
            callback(node.data);
            const nodes = inwards ? node.outgoing : node.incoming;
            collections.forEach(nodes, (entry) => this._traverse(entry.value, inwards, seen, callback));
        }