interface PageInfo {
  hasNextPage: boolean;
  endCursor: string;
}

interface Connection<Edge> {
  pageInfo: PageInfo;
  edges: Edge[];
}

interface Response<Node> {
  hasNextPage: boolean;
  endCursor: string;
  nodes: Node[];
}

const extractConnectionInfo = <Edge extends { node?: Node }>({ edges, pageInfo }: Connection<Edge>): Response<Node>  => {
   ...parsing work
}

extractConnectionInfo

nodes

node

// type of nodes is "unknown[]"
const { nodes } = extractConnectionInfo({ edges, pageInfo });

unknown[]

type Node = {
  id: string,
};

type Edge<NodeType extends Node> = {
  node: NodeType,
};

type Connection<NodeType extends Node, EdgeType extends Edge<NodeType> = Edge<NodeType>> = {
  edges: EdgeType[],
  pageInfo: PageInfo,
};

type NodeTypeFromConnection<ConnectionType> = ConnectionType extends Connection<infer NodeType> ? NodeType : never;

function extractConnectionInfo<ConnectionType extends Connection<unknown>>(connection: ConnectionType): { nodes: Array<NodeTypeFromConnection<ConnectionType>> } {
  ...
}

Connection<unknown>

엣지가 왜 nullable 이여야해요?

flatMap

node

id

type Node = unknown