Is it obligatory to indicate the content type in the responses to the client?

Question

Node.js

Tell me, is it necessary to write in the answer to the client?
res.setHeader("Content-Type", "text/css")
And why is it always indicated in books on node?

Answer 1

The Content-Type header is optional, but the Content-Type is better if known.
This header is needed so that the browser understands what type of content the server returns.
Here is what they write about this in the documentation ( https://nodejs.org/api/http.html#http_response_wri... ), if this header is not specified "it will switch to implicit header mode and flush the implicit headers", i.e. .e. the node will specify it implicitly.