Error-first callback in Node.js
The error-first callback, also called as errorback gives the error and data. It takes a few arguments, the first one being the error object and others being the data. The error-first callback pattern has many advantages: since it is consistent, leads to more adoption, if there is no reference to the data, there is no need to process it. If there is no error, the callback is called with null as the first argument.