I'm learning node, and one thing I can't seem to figure out is callback signatures. It seems that most callbacks are typically of the form
function myCallback(err, doc)
which makes sense. But then I come across some other modules, like node-easyimage, which casually mention examples with different signatures, like
function myCallback(err, stdout, stderr)
There is no mention of which APIs expect which format of callbacks, so I end up digging through the code. But given that callback signatures are almost never mentioned; I feel like there is an unspoken rule that I haven't read. Is there?
There's no standard approach unfortunately, so you'll just have to get accustomed to the techniques each package uses. This is a general Javascript issue and not just node.js, which is why TypeScript for example has such appeal.
While it is true that there is no standard, the Node community is slowly coalescing around a convention of callback(error, results), where results could be a String, Array, Object, etc. depending on the API.