CODEWITHSUNDEEP
node.jsexpress
Salah Eddine Taouririt
Salah Eddine Taouririt

Reputation: 26415

How to debug a hanging express server?

In the next example, the application is using a m middleware.

const express = require("express");
const app = express();

const m = () => (req, res, next) => {
  next();
};

app.use(m());

app.get("/", (req, res) => {
  res.sendStatus(200);
});

app.listen(5000);

if I (by accident) passed the function itself instead of the result of calling it: 

-app.use(m()); 
+app.use(m); // causes express server hangs

the server will hangs.

How can I debug this issue?

Upvotes: 2

Views: 1385

Answers (1)

jfriend00
jfriend00

Reputation: 707436

m is a function that returns a middleware function when you call it.

To get the middleware function you have to call it with m(). If you just pass m, then that's not a middleware function and executing it just immediately returns another function and never calls next() so when express executes m, it runs, immediately returns another function (which is ignored by Express) and your request is never handled.

Also, there's NO reason for making a function that returns a function in the case you show either. Just make a function and pass a reference to that function as middleware.

function m(req, res, next) {
    next();
}

app.use(m);

Or inline:

app.use(function(req, res, next) {
   next();
});

Upvotes: 1

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