build/lib/tsb/utils.ts/Graph/lookupOrInsertNode
class Graph:        lookupOrInsertNode(data: T): Node<T> {
            const key = this._hashFn(data);
            let node = collections.lookup(this._nodes, key);

            if (!node) {
                node = newNode(data);
                this._nodes[key] = node;
            }

            return node;
        }