Request Context in Node.js

GraphQL context is commonly used to expose request-scoped dependencies to resolvers.

For example, a request context might contain:

{
  user: authenticatedUser,
  requestId: "req-123",
  userService,
  postService,
  loaders
}

A resolver can then access those values:

const resolvers = {
  Query: {
    me: (_, __, context) => {
      return context.user;
    }
  }
};

Context is especially useful for authentication because authentication middleware can establish the current user before GraphQL execution begins.

It can also hold request-specific DataLoader instances. This is important because DataLoader caches should normally be scoped appropriately to a request rather than accidentally shared across unrelated users.

Avoid putting global mutable state into context simply because context is convenient. Application-wide configuration, immutable service instances, and request-specific information have different lifecycles and should be modeled accordingly.

A clean context design makes dependencies explicit and reduces the temptation to import global mutable variables from everywhere in the resolver layer.

Request Context Example

const server = new ApolloServer({
  typeDefs,
  resolvers
});

const context = async ({ req }) => {
  const user = await authenticateRequest(req);

  return {
    user,
    requestId: req.headers["x-request-id"],
    userService,
    postService
  };
};

💡 The context function creates values associated with the current request. Resolvers can then access authentication information and application services through the context argument. In production, authentication failures, request IDs, and dependency lifecycles should be handled consistently.

Key Takeaways

GraphQL context is useful for request-scoped dependencies.
Authentication information is commonly exposed through context.
Request-specific loaders should have appropriate request lifecycles.
Avoid using context as an uncontrolled global-state container.

Knowledge Check

Why is request-scoped context useful for GraphQL authentication?

Request Context in Node.js

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