NodeJS Advanced Topics Syllabus

What are the three root operation types in GraphQL?

Query (read data), Mutation (write/modify data), and Subscription (receive real-time updates, typically over WebSockets).

What is a GraphQL schema?

A strongly typed contract, written in the Schema Definition Language (SDL), that defines the types, fields, and root operations (Query, Mutation, Subscription) the API exposes.

What is a resolver in GraphQL?

A function that returns the value for a particular field in the schema; GraphQL calls resolvers to fetch or compute the data for each requested field.

What arguments does a GraphQL resolver function receive?

Four arguments: parent (the result of the parent field), args (the field's arguments), context (shared per-request data like auth/DB connections), and info (query AST/execution metadata).

In GraphQL SDL, what does the '!' symbol after a type mean?

It marks the field as non-nullable (required); for example, name: String! means name must always return a non-null String.

In GraphQL SDL, what does '[String!]!' mean?

A non-nullable list of non-nullable Strings: the list itself cannot be null, and none of its elements can be null.

List the five built-in scalar types in GraphQL.

Int, Float, String, Boolean, and ID.

What is the difference between a GraphQL 'type' and an 'input' type?

An object type (type) describes data returned by the API; an input type (input) is used to pass structured arguments into queries and mutations and cannot have resolvers or circular object references the same way.

What is Apollo Server?

A popular, spec-compliant open-source GraphQL server library for NodeJS that lets you define a schema and resolvers and serve them over HTTP, with support for integrations, subscriptions, and tooling.

What are the two required inputs to construct an Apollo Server (or most GraphQL servers) in NodeJS?

typeDefs (the schema written in SDL) and resolvers (the map of functions that provide data for the schema's fields).

How do you start a standalone Apollo Server (v4) in NodeJS?

Create the server with new ApolloServer({ typeDefs, resolvers }), then call startStandaloneServer(server, { listen: { port } }), which returns the URL it is listening on.

What is GraphQL introspection?

A built-in feature that lets clients query the schema itself (via __schema and __type) to discover available types, fields, and operations; it powers tools like GraphiQL and Apollo Sandbox.

How are the 'context' objects typically used in a GraphQL server?

The context is created per request and holds shared data such as the authenticated user, database connections, and dataloaders, making it available to every resolver during that request.

What is the N+1 problem in GraphQL and one way to solve it?

When resolving a list, each item triggers a separate downstream query (1 for the list + N for items), causing many redundant calls. DataLoader batches and caches these requests within a single tick to reduce them.

How do you integrate Apollo Server with an existing Express application?

Use the expressMiddleware from @apollo/server/express4: create and await server.start(), then mount app.use('/graphql', cors(), express.json(), expressMiddleware(server, { context })) on your Express app.

Why would you integrate GraphQL into Express rather than run it standalone?

To reuse existing Express middleware (auth, logging, CORS, body parsing), serve REST and GraphQL from the same server, and add custom routes alongside the /graphql endpoint.

Which HTTP method and status code does a typical GraphQL-over-HTTP request use?

Queries and mutations are usually sent as HTTP POST to a single /graphql endpoint, and even errors commonly return HTTP 200 with an 'errors' array in the JSON response body.

What is serverless computing?

A cloud execution model where the provider dynamically manages server provisioning and scaling; developers deploy functions or code that run on demand, and billing is based on actual execution rather than pre-provisioned capacity.

What does 'Function as a Service' (FaaS) mean?

A serverless model where you deploy individual functions that the cloud provider runs in response to events, automatically scaling and charging only for execution time. AWS Lambda, Azure Functions, and Google Cloud Functions are examples.

Give three benefits of serverless architectures.

No server management, automatic scaling with demand, pay-per-use billing (no cost when idle), and faster time to market for individual functions.

What is a 'cold start' in serverless?

The added latency when a function is invoked after being idle, because the platform must initialize a new execution environment (container/runtime) before running the code; subsequent 'warm' invocations reuse it and are faster.

Name two common limitations of serverless functions.

Execution time limits (e.g., AWS Lambda caps at 15 minutes), cold-start latency, statelessness (no reliable local persistence between invocations), and vendor lock-in.

What is AWS Lambda?

Amazon's serverless FaaS compute service that runs your code in response to events and automatically manages the underlying compute; you upload a function and Lambda handles scaling, availability, and execution.

What is the signature of a NodeJS AWS Lambda handler function?

exports.handler = async (event, context) => { ... }; where event carries the invocation payload/trigger data and context provides runtime info (request ID, remaining time, memory).

How is an AWS Lambda function typically triggered?

By event sources such as API Gateway (HTTP requests), S3 events, DynamoDB Streams, SNS/SQS messages, EventBridge/CloudWatch scheduled events, and direct SDK invocations.

What is the maximum execution timeout for an AWS Lambda function?

15 minutes (900 seconds); memory is configurable (from 128 MB up to 10,240 MB), and CPU scales proportionally with allocated memory.

How does AWS Lambda pricing work?

You are charged per request plus for compute measured in GB-seconds, i.e., allocated memory multiplied by execution duration; there is no charge when the function is not running (a generous free tier also applies).

What is the Serverless Framework?

An open-source, provider-agnostic CLI and framework for developing, packaging, and deploying serverless applications (functions and their infrastructure) using a declarative configuration file, most commonly with AWS Lambda.

What configuration file does the Serverless Framework use, and what does it define?

serverless.yml (or .ts/.js/.json), which declaratively defines the provider, functions, their event triggers, resources, plugins, and environment configuration for the deployment.

In serverless.yml, what does the 'functions' section define versus the 'events' within it?

The 'functions' section lists each deployable function and its handler; the 'events' under a function define the triggers (e.g., http, schedule, s3, sqs) that invoke that function.

Which Serverless Framework CLI command deploys your service to the cloud, and how do you remove it?

'serverless deploy' (or 'sls deploy') packages and provisions the service (on AWS via CloudFormation); 'serverless remove' tears down all the deployed resources.