Node.js Error First Callback - Error Handling

First I would like to share about “What is callback?” and after share about “Error first callback” in Node.js.

A callback is an asynchronous function which is being called when an Ajax request/call is completed.

The Node.js is using much more callback because the entire node APIs use it.

What is “Error First Callback” in Node.js?

The “Error first callback” is used to pass an error and data. The first argument to these functions is an error object and the second argument represents to the success data. So, you can check the first argument as an error object and the second argument as data. If nothing wrong happen in your app use data.

Example,

var successCallback = function(callback) {
  this._get(function(error, data) {
    if (error) {
      console.log(error);
      return;
    }else{
      callback(null, data);
    }
  });
};

The error first callback pattern just requires that your function accepted two parameters and the first is an error and second one is the data.

The error is an object not a function and the error object containing the related information an also we can set a null value at the place of error object if there is no error occurred in the apps.

Summary,

Only Two Rules for defining an error first callback,

1.      The first argument of the callback is reserved for an error object.

2.      The second argument of the callback is reserved for response data (this is only for successful response).

References,

https://nodejs.org/api/errors.html

http://callbackhell.com/

http://fredkschott.com/post/2014/03/understanding-error-first-callbacks-in-node-js/