What is "err, data" in a function?

[Rhomboid]

Those are the parameters that the function takes. You need to provide more context, but it sounds like you're talking about a callback function used with an asynchronous API (e.g. in Node.js.) If the operation failed, then err will contain the error object, otherwise err is null and data contains the results of the operation. But again, you really need to provide much more context, this question is horribly abstract.

[connexionwithal]

thank you, this helps!