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LESSON 01 / 2·2 min readIntermediate

The Express request lifecycle

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01 Understand02 Recall03 Prepare

Understand the concept

Express handles requests through a sequence of registered middleware and route handlers. Middleware can inspect or change the request, stop it with a response, or pass it onward. The order of registration matters because later handlers see the result of earlier ones.

Important ideas

  • Matching middleware runs in registration order.

  • A route handler calls the service and sends a response.

  • Middleware must send a response or call next(); otherwise the request can hang.

  • A router groups related routes; controllers translate HTTP details while services implement business rules.

Request flow:

  1. Client sends a request; Express matches the registered path and middleware.
  2. Parsing middleware reads permitted input and authentication identifies the caller.
  3. Authorization and validation reject requests that should not continue.
  4. The controller calls business logic in a service.
  5. The service completes database or external work.
  6. A response is sent, or an error is forwarded to error middleware.
PAUSE & RECALL

Can you explain it without the notes?

What happens during an Express request?

Use your own words. Explain an example and one limitation before checking the explanation.

Check your explanation

Express handles requests through a sequence of registered middleware and route handlers. Middleware can inspect or change the request, stop it with a response, or pass it onward. The order of registration matters because later handlers see the result of earlier ones.

CONNECT IT TO YOUR INTERVIEW

Turn this concept into a clear answer.

  • Explain the full path from request parsing and authentication to validation, business logic and one final response.

What happens during an Express request?

Express·Express lifecycle

Express handles requests through a sequence of registered middleware and route handlers. Middleware can inspect or change the request, stop it with a response, or pass it onward. The order of registration matters because later handlers see the result of earlier ones.

Intermediate2 min read
Practice this concept
YOUR NEXT STEP

Keep connecting the ideas.

Next lesson: How should Express handle errors?
LESSON MAPExplore the learning path

Adapted from 02_NODE_EXPRESS_HTTP.md · “What happens during an Express request?”. Examples are study fragments; framework behavior can depend on your version.