What does express.urlencoded do anyway?

I finally found out what this bit of middleware in most express apps does, and wanted to document it

app.use(
  express.urlencoded({
    extended: true,
  })
);

The documentation says:

This is a built-in middleware function in Express. It parses incoming requests with JSON payloads and is based on body-parser.

Returns middleware that only parses JSON and only looks at requests where the Content-Type header matches the type option. This parser accepts any Unicode encoding of the body and supports automatic inflation of gzip and deflate encodings.

A new body object containing the parsed data is populated on the request object after the middleware (i.e. req.body), or an empty object ({}) if there was no body to parse, the Content-Type was not matched, or an error occurred.

👆This makes very little sense to me, but I want to thank Deepal Jayasekara for clarifying this as:

✅ express.urlencoded middleware is used only for parsing request body of content-type x-www-form-urlencoded

For eg: Assuming you have an app running on port 8080, and you have a request like this:

curl -d"foo=bar" -H"Content-Type: application/x-www-form-urlencoded" http://localhost:8080

You will only be able to access req.body.foo if you have the express.urlencoded middleware.

BTW, if you’re still using body-parser to do this, note that it has been deprecated and express encourages you to use express.json() and express.urlencoded methods that come with express now.