GraphQL Interview Questions and Answers for 5 years experience

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GraphQL Interview Questions & Answers (5 Years Experience)

  1. What is GraphQL and how does it differ from REST?

    • Answer: GraphQL is a query language for APIs and a runtime for fulfilling those queries with your existing data. Unlike REST, which uses fixed endpoints returning pre-defined data structures, GraphQL allows clients to request exactly the data they need, reducing over-fetching (receiving unnecessary data) and under-fetching (requiring multiple requests to get all needed data). GraphQL uses a strongly-typed schema for better data validation and introspection, and it often uses a single endpoint for all data access, simplifying client interactions. REST typically relies on multiple endpoints, each serving a specific resource.

  2. Explain the concept of a GraphQL schema.

    • Answer: The GraphQL schema is a formal description of the data your API provides. It's written using the Schema Definition Language (SDL) and defines the types of data, their fields, relationships between types (e.g., using interfaces, unions, and enums), and the arguments that can be passed to queries and mutations. The schema acts as a contract between the client and the server, ensuring that both understand the available data and how to interact with it. It allows for static analysis and validation.

  3. What are the different types in GraphQL?

    • Answer: GraphQL supports scalar types (e.g., Int, Float, String, Boolean, ID), object types (representing complex data structures), interface types (defining shared fields across multiple object types), union types (allowing a field to return one of several object types), enum types (defining a set of possible values), and list types (representing arrays of values).

  4. Describe the difference between queries and mutations in GraphQL.

    • Answer: Queries are used to fetch data from the server. They are read-only operations. Mutations are used to modify data on the server; they are write operations (e.g., creating, updating, or deleting data). Queries are typically used for retrieving information, while mutations are used for actions that change the application's state.

  5. Explain how resolvers work in GraphQL.

    • Answer: Resolvers are functions that fetch the data for a particular field in your GraphQL schema. They take arguments from the query/mutation and return the corresponding data. They act as the bridge between the GraphQL schema and your underlying data sources (e.g., databases, APIs). Resolvers can be chained together to handle nested fields.

  6. What is a GraphQL subscription?

    • Answer: Subscriptions provide a way for clients to receive real-time updates from the server. When a specific event occurs on the server, the subscribed client is automatically notified with the new data. This enables features like real-time chat, live dashboards, and other reactive applications.

  7. How do you handle errors in GraphQL?

    • Answer: GraphQL allows you to include error details within the response, providing context to the client about what went wrong. You can customize error messages and include specific error codes. Proper error handling is crucial for debugging and providing helpful feedback to clients. Tools like Apollo Client provide helpful error handling capabilities.

  8. Explain the concept of pagination in GraphQL.

    • Answer: Pagination is essential for efficiently handling large datasets. Instead of returning all results at once, which can be slow and resource-intensive, pagination allows clients to request data in smaller, manageable chunks. Common approaches include using `offset` and `limit` arguments or using cursors to navigate through the data.

  9. What are some common GraphQL tools you've used?

    • Answer: (This answer will vary depending on experience, but should include a few of the following:) Apollo Client, Apollo Server, GraphQL Yoga, Hasura, Prisma, GraphiQL, and various IDE extensions.

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