What's the point of middlewares replacing built in Express.js functions?

Question

There's quite a list of Express.js middlewares replacing built-in functions. For example:

body-parser - Parse HTTP request body. Replaces built-in function express.bodyParser

What do they mean when they say "replaces built-in function"? Do those replacements provide any improvement on top of built-in versions? I mean I do not see any point in using additional modules, if they don't. I'm asking 'cause I do not see it mentioned anywhere, at least in the middleware documentation.

Answer 1

It means that it overrides default behavior or object natively given in the app.

Excerpt from the doc, for example the res.json :

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

...

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

The body-parser in question is useful for me, I used it to recover the data transmitted in an post form for example.

Since the update to express v4 original builtin functions were separated into standalone modules . Now each module is independent but still included as a dependency in the package.json of express.js .

It is somewhat confusing.