Last modified: April 23, 2025

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Middleware

Functions that run during each request (or a subset of requests):

• These functions are chained together, each one calling the next function (in the variable next)
  • At the end they finally call your API endpoint handler (e.g., app.get("/users", …))
• They generally either:
  • Modify the request
  • Modify the response
  • Log something

Structure of a middleware function:

app.use(function (req, res, next) {
    // modify req, res, or log something
    next(); // call the next function (middleware or handler)
});