Node.js runs JavaScript outside the browser. Express provides a lightweight way to define routes and middleware for HTTP requests. A useful API has a clear contract: clients know which requests are accepted, which responses to expect and how errors are represented.
Design around resources
Choose route names and HTTP methods that reflect the operation. A collection endpoint may list or create records; an item endpoint may read or update one record. Use status codes consistently and return a predictable JSON structure so clients can handle each outcome.
Validate at the server boundary
Every client value is untrusted, even when a React form checks it. Validate required fields, types, allowed values and reasonable lengths in the API. Check that the caller is permitted to access the requested record. A hidden button or protected frontend route is not server-side authorization.
Handle asynchronous failures
Database queries and network operations can fail. Await asynchronous work and route failures into deliberate error handling. Return an appropriate response without exposing stack traces, environment configuration, database internals or secrets. Log enough context for authorized troubleshooting while avoiding sensitive personal information.
Test the contract
Test valid requests, malformed input, missing records and access failures. Verify the response body and status code for each case. Documentation should state expected fields and behavior, not just list URLs.
Practice exercise
- Design list, detail, create and update routes for a fictional resource.
- Write server-side validation rules for each request body.
- Choose status codes and response shapes for success and failure.
- Add tests for valid input, invalid input and a missing record.
- Confirm no error response reveals internal implementation details.
Continue with the MERN Full Stack Developer Course and the Node.js and Express topic guide.