Question

Might be obvious, but still I’m lacking here of the basic knowledge.

So inside controllers, can both be used, or is it always Javascript, so both are the same?

Answer 1

In Rails 3.1 the only difference I can spot is that the if formatter is js, then the answer is sent as plain text. If it is json then it is encoded as json.

if format.json

format.json {
  render :json => @accounts.map(&:attributes)
}

server send:

data:application/json;base64,

if format.js

format.js {
  render :json => @accounts.map(&:attributes)
}

server send:

[{"id":33,"email":"[e-mail]"}]