Skip to main content

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,
By Anil Singh | Rating of this article (*****)

Popular posts from this blog

List of Countries, Nationalities and their Code In Excel File

Download JSON file for this List - Click on JSON file    Countries List, Nationalities and Code Excel ID Country Country Code Nationality Person 1 UNITED KINGDOM GB British a Briton 2 ARGENTINA AR Argentinian an Argentinian 3 AUSTRALIA AU Australian an Australian 4 BAHAMAS BS Bahamian a Bahamian 5 BELGIUM BE Belgian a Belgian 6 BRAZIL BR Brazilian a Brazilian 7 CANADA CA Canadian a Canadian 8 CHINA CN Chinese a Chinese 9 COLOMBIA CO Colombian a Colombian 10 CUBA CU Cuban a Cuban 11 DOMINICAN REPUBLIC DO Dominican a Dominican 12 ECUADOR EC Ecuadorean an Ecuadorean 13 EL SALVADOR

39 Best Object Oriented JavaScript Interview Questions and Answers

Most Popular 37 Key Questions for JavaScript Interviews. What is Object in JavaScript? What is the Prototype object in JavaScript and how it is used? What is "this"? What is its value? Explain why "self" is needed instead of "this". What is a Closure and why are they so useful to us? Explain how to write class methods vs. instance methods. Can you explain the difference between == and ===? Can you explain the difference between call and apply? Explain why Asynchronous code is important in JavaScript? Can you please tell me a story about JavaScript performance problems? Tell me your JavaScript Naming Convention? How do you define a class and its constructor? What is Hoisted in JavaScript? What is function overloadin

React | Encryption and Decryption Data/Text using CryptoJs

To encrypt and decrypt data, simply use encrypt () and decrypt () function from an instance of crypto-js. Node.js (Install) Requirements: 1.       Node.js 2.       npm (Node.js package manager) 3.       npm install crypto-js npm   install   crypto - js Usage - Step 1 - Import var   CryptoJS  =  require ( "crypto-js" ); Step 2 - Encrypt    // Encrypt    var   ciphertext  =  CryptoJS . AES . encrypt ( JSON . stringify ( data ),  'my-secret-key@123' ). toString (); Step 3 -Decrypt    // Decrypt    var   bytes  =  CryptoJS . AES . decrypt ( ciphertext ,  'my-secret-key@123' );    var   decryptedData  =  JSON . parse ( bytes . toString ( CryptoJS . enc . Utf8 )); As an Example,   import   React   from   'react' ; import   './App.css' ; //Including all libraries, for access to extra methods. var   CryptoJS  =  require ( "crypto-js" ); function   App () {    var   data

25 Best Vue.js 2 Interview Questions and Answers

What Is Vue.js? The Vue.js is a progressive JavaScript framework and used to building the interactive user interfaces and also it’s focused on the view layer only (front end). The Vue.js is easy to integrate with other libraries and others existing projects. Vue.js is very popular for Single Page Applications developments. The Vue.js is lighter, smaller in size and so faster. It also supports the MVVM ( Model-View-ViewModel ) pattern. The Vue.js is supporting to multiple Components and libraries like - ü   Tables and data grids ü   Notifications ü   Loader ü   Calendar ü   Display time, date and age ü   Progress Bar ü   Tooltip ü   Overlay ü   Icons ü   Menu ü   Charts ü   Map ü   Pdf viewer ü   And so on The Vue.js was developed by “ Evan You ”, an Ex Google software engineer. The latest version is Vue.js 2. The Vue.js 2 is very similar to Angular because Evan You was inspired by Angular and the Vue.js 2 components looks like -

Encryption and Decryption Data/Password in Angular

You can use crypto.js to encrypt data. We have used 'crypto-js'.   Follow the below steps, Steps 1 –  Install CryptoJS using below NPM commands in your project directory npm install crypto-js --save npm install @types/crypto-js –save After installing both above commands it looks like  – NPM Command  1 ->   npm install crypto-js --save NPM Command  2 ->   npm install @types/crypto-js --save Steps 2  - Add the script path in “ angular.json ” file. "scripts" : [                "../node_modules/crypto-js/crypto-js.js"               ] Steps 3 –  Create a service class “ EncrDecrService ” for  encrypts and decrypts get/set methods . Import “ CryptoJS ” in the service for using  encrypt and decrypt get/set methods . import  {  Injectable  }  from   '@angular/core' ; import   *   as   CryptoJS   from   'crypto-js' ; @ Injectable ({    providedIn:   'root' }) export   class   EncrDecrS