What does `app.use(bodyParser.json())` do?

Question

For:

bodyParser.urlencoded({extended: ...})

my research shows me that if extended: true, then you can parse nested objects, or generally any type. However, if you set extended: false, then you can only parse strings or arrays. But what does ...

app.use(bodyParser.json())

mean exactly? I mean, yes... I know the docs mention that it parses json. But I am still confused. I have noticed applications that set extended: true do NOT use bodyParser.json() at all. But applications that extended: false tend to use bodyParser.json(). Why is this? At the end of the day, both applications are able to parse json.

Secondly, which is the recommended approach?

Tound

Answer 1

Okay, contrary to what I previously thought, further research shows that extended: true and app.use(bodyParser.json()) can be used together. So it is not only extended: false that uses it. The statement app.use(bodyParser.json()) is to be used independently, whether you set extended as true or false.

• app.use(bodyParser.json()) basically tells the system that you want json to be used.

• bodyParser.urlencoded({extended: ...}) basically tells the system whether you want to use a simple algorithm for shallow parsing (i.e. false) or complex algorithm for deep parsing that can deal with nested objects (i.e. true).

Have a look at the docs (i.e. https://expressjs.com/en/guide/migrating-4.html) for the example.

Tound

Answer 2

URL encoding and JSON encoding both allow to convert a (nested) object to string, but the format is different. An URL encoded string is in general not a valid JSON string.

One application may use one encoding method, and another the other. As long as they don't mix the two, it will work.

Subotica

Can one application set extended as true and yet still have app.use(bodyParse.json())? Or does the latter always go with extended being false? But interestingly, both seem to work for json parsing. – Tound

Answer 3

bodyParser.json returns middleware that only parses JSON. 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).

Cuthburt