Before: Callback function implementation that does not use guard return statements. After: Callback function implementation that uses guard return statements. Inspiration, http://www.bennadel.com/blog/2323-Use-A-Return-Statement-When-Invoking-Callbacks-Especially-In-A-Guard-Statement.htm

after.js

if (err) {
	return callback(err);
}

if (!udfDocument) {
	var msg = 'Could not find UDF document for importId: ' + udfId;
	return callback(new Error(msg));
}

return callback(udfDocument);

before.js

if (err) {
	callback(new Error(err));
}
else if (!udfDocument) {
	var msg = 'Could not find UDF document for importId: ' + udfId;
	callback(new Error(msg));
} else {
	callback(udfDocument);
}