Syntax
- Each callback must be written with this syntax:
- function callback(err, result [, arg1[, …]])
- This way, you are forced to return the error first, and can’t ignore handling them later on.
null
is the convention in absence of errors
- callback(null, myResult);
- Your callbacks can contain more arguments than err and result, but it’s useful only for a specific set of functions (waterfall, seq, …)
- callback(null, myResult, myCustomArgument);
- And, of course, send errors. You must do it, and handle errors (or at least log them).
- callback(err);