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Introduction to Hooks in React

Technological change is rapidly impacting our present and our prospects for the future, and so are frontend frameworks, which are emerging at a very fast pace these days. And in many ways, React, the most popular framework amongst the JavaScript community, is turning out to be unstoppable.   Many of us have already played around with Hooks or have at least heard about them. But there are still many who are probably yet to take the time or have had the chance to experiment with them.  No worries, sooner or later you will find yourself diving into Hooks.  In this article, you will learn about the term, ‘Hooks’, and the reasons why you should use them in your future projects. Furthermore, you will learn about how you can use React Hooks in the best possible manner to build some awesome features in your projects and write cleaner code.  What exactly is a Hook? Hooks are just regular JavaScript functions. In layman terms, hooks provide a way to use functionalities such as context or state, which could earlier only be achieved through classes, and now can easily be done using function components. React Hooks enable functional components to attach local state with it, and this state will be preserved by React when the component re-renders. Hence, this allows React to be used without classes. While working with function components in React, we sometimes need to add state to it. In order to achieve that (to use setState() and states), we have to convert our function component into class one. With the help of Hooks, we can use the state in Function Components, without the use of classes. A practical view There are two approaches to create a React component. One is using functions and the other is using classes. There is always a question in mind that “When do I use one v/s the other?” Let us assume we have a simple class component and then we will convert it to a functional one with hooks and see the difference. Component without Hook: Class Componentimport React, { Component } from'react';  classGreetingextendsComponent {     state = {         text: ''”     }  handleChange= (e) => {  this.setState({ text: e.target.value })     }  render() {  return (             <input  value={this.state.text}  onChange={this.handleChange}             />         )     }  }  exportdefaultGreeting; Components with Hook:Functional Component: import React, { useState } from'react';  exportdefault () => {  const [text, setText] =useState('');  return (         <input  value={text}  onChange={(e) =>{ setText(e.target.value) }}         />     );  }Advantages: Readable Lesser Code. Overall Optimized component Writing a Functional component with state Writing complex components became easier Handling events & logics in functional components. Performance boost up with Functional Components  If you disagree with any of the above, you can play with it in practice. I’m sure that would change your mind! Types of Hooks Now, let us understand the power of hooks with some cool examples that will describe some basic Hooks which are: useState() useEffect() Custom Hooks (Building Your Own Hooks) State Hook In React, we all are quite familiar with how the state is generally defined. If not, I’d recommend you to refresh your memory of State here. this.state= {     name: Steve Marley  }; While state issimilar to props, we know that state is controlled by a component. Traditionally, state is generally defined by writing a class where “this.state” is used to initialize a class. Let us take an example of class Component named (MyComponent): classMyComponentextendsReact.component {  constructor(props)  super(props);  this.state= {         name: Steve Marley     }  } In class components, it isreally hard to reuse stateful logic between components and complex class components become hard to read and even harder to understand!! React hooks help us to get rid of all that old-fashioned class stuff by making use of useState().  Now, this is important to note that in a functional component there is no concept of objects and objects being set as context (like we do in classes), so we can’t assign anything or read this.state. Instead, we call the useState Hook directly inside our functional component: This will become something like this: import{ useState } from'react'; // line 1  functionMyComponent() {  const [name, setName] =useState(‘Steve Marley');   // line 2  } Let us understand this code line by line: In line1: there is a new method imported here called useState. What is useState and how do we use it? Well, useState is the React Hook that will allow us to access and manipulate state in our existing component. Therefore, in this approach, we do not have to extend our Component as we did in previous code. And that’s it! It is worth noting that we are playing with states outside a class in the component directly as shown: import{ useState } from'react'; functionMyComponent() {  const [name, setName] =useState(‘Steve Marley’);  return     <div>         <p>Heyyyyy!! {name}</p>     </div>  }Deeper explanation In class Component, we initialized the name state to 'Steve Marley' by setting this.state to { name: Steve Marley } in the constructor whereas in Functional componentthe only argument to the useState() Hook is the initial state.  Unlike with classes, the state does not have to be an object. We can keep a number or a string if that is all we need. What does useState return?It returns two variables in the array [name, setName]  where “name” is the state variable and it could be anything, and setName is the function call (can be named anything), which updates the state by providing a new state. If you are not familiar with the above syntax, please read array destructuring in JavaScript. In our example we have declared a state variable called name and set it to Steve Marley. React will remember its current value between re-renders and provide the most recent one to our function. If we want to update the current name, we can call setName. This is a way to “preserve” some values between the function calls so in other words useState is a new way to use the exact same capabilities that this.state provides in a class. Normally, variables “disappear” when the function exits but state variables are preserved by React. It is worth noticing that now our component (functional component) looks pretty simple, crisp and it does not have the level of complexity that a class component normally has. Effect Hook So far, we have seen extracting stateful logic with the help of hooks and defining/setting states inside a component. But what about managing the DOM from one component to another? Or fetching the data through an API? Or handling Events? All these operations which are quite familiar to usare effects!  The Effect Hook adds the ability to perform side effects from a functional component. It is a lifecycle Hook that combinescomponentDidMount, componentDidUpdate, and componentWillUnmount in React classes but unified them into a single API. useEffect(() => {  // Do some task here  }); By calling this hook, we are simply telling our component to perform some tasks after render like Data fetching, setting up a subscription, and manually changing the DOM in our React components. Let us understand this with an example: import React, { useState, useEffect } from"react"; exportdefaultfunctionGetData() {  const [myData, setData] =useState([]);  useEffect(() => {  fetch("https://jsonplaceholder.typicode.com/todos/1")  .then(response=>response.json())  .then(myData=>setData(myData));     });  retu
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Introduction to Hooks in React

17
Introduction to Hooks in React

Technological change is rapidly impacting our present and our prospects for the future, and so are frontend frameworks, which are emerging at a very fast pace these days. And in many ways, React, the most popular framework amongst the JavaScript community, is turning out to be unstoppable.   

Many of us have already played around with Hooks or have at least heard about them. But there are still many who are probably yet to take the time or have had the chance to experiment with them.  No worries, sooner or later you will find yourself diving into Hooks.  

In this article, you will learn about the term, Hooks, and the reasons why you should use them in your future projects. Furthermore, you will learn about how you can use React Hooks in the best possible manner to build some awesome features in your projects and write cleaner code.  

What exactly is a Hook? 

Hooks are just regular JavaScript functions. In layman terms, hooks provide a way to use functionalities such as context or state, which could earlier only be achieved through classes, and now can easily be done using function components. 

React Hooks enable functional components to attach local state with it, and this state will be preserved by React when the component re-renders. Hence, this allows React to be used without classes. 

While working with function components in React, we sometimes need to add state to it. In order to achieve that (to use setState() and states), we have to convert our function component into class one. With the help of Hooks, we can use the state in Function Components, without the use of classes. 

A practical view 

There are two approaches to create a React component. One is using functions and the other is using classes. There is always a question in mind that “When do I use one v/s the other?” 

Let us assume we have a simple class component and then we will convert it to a functional one with hooks and see the difference. 

Component without Hook: Class Component

import React, { Component } from'react'; 
classGreetingextendsComponent { 
   state = { 
       text: ''” 
   } 
handleChange= (e) => { 
this.setState({ text: e.target.value }) 
   } 
render() { 
return ( 
           <input 
value={this.state.text} 
onChange={this.handleChange} 
           /> 
       ) 
   } 
} 
exportdefaultGreeting; 

Components with Hook:Functional Component: 

import React, { useState } from'react'; 
exportdefault () => { 
const [text, setText] =useState(''); 
return ( 
       <input 
value={text} 
onChange={(e) =>{ setText(e.target.value) }} 
       /> 
   ); 
}

Advantages: 

  • Readable 
  • Lesser Code. 
  • Overall Optimized component 
  • Writing a Functional component with state 
  • Writing complex components became easier 
  • Handling events & logics in functional components. 
  • Performance boost up with Functional Components  

If you disagree with any of the above, you can play with it in practice. I’m sure that would change your mind! 

Types of Hooks 

Now, let us understand the power of hooks with some cool examples that will describe some basic Hooks which are: 

  • useState() 
  • useEffect() 
  • Custom Hooks (Building Your Own Hooks) 

State Hook 

In React, we all are quite familiar with how the state is generally defined. If not, I’d recommend you to refresh your memory of State here

this.state= { 
   name: Steve Marley 
}; 

While state issimilar to props, we know that state is controlled by a component. Traditionally, state is generally defined by writing a class where “this.state” is used to initialize a class. 

Let us take an example of class Component named (MyComponent): 

classMyComponentextendsReact.component { 
constructor(props) 
super(props); 
this.state= { 
       name: Steve Marley 
   } 
} 

In class components, it isreally hard to reuse stateful logic between components and complex class components become hard to read and even harder to understand!! 

React hooks help us to get rid of all that old-fashioned class stuff by making use of useState().  

Now, this is important to note that in a functional component there is no concept of objects and objects being set as context (like we do in classes), so we can’t assign anything or read this.state. Instead, we call the useState Hook directly inside our functional component: 

This will become something like this: 

import{ useState } from'react'; // line 1 
functionMyComponent() { 
const [name, setName] =useState(‘Steve Marley');   // line 2 
} 

Let us understand this code line by line: 

In line1: there is a new method imported here called useState. 

What is useState and how do we use it? 

Well, useState is the React Hook that will allow us to access and manipulate state in our existing component. Therefore, in this approach, we do not have to extend our Component as we did in previous code. 

And that’s it! It is worth noting that we are playing with states outside a class in the component directly as shown: 

import{ useState } from'react';
functionMyComponent() { 
const [name, setName] =useState(‘Steve Marley’); 
return 
   <div> 
       <p>Heyyyyy!! {name}</p> 
   </div> 
}

Deeper explanation 

In class Component, we initialized the name state to 'Steve Marley' by setting this.state to { name: Steve Marley } in the constructor whereas in Functional componentthe only argument to the useState() Hook is the initial state.  

Unlike with classes, the state does not have to be an object. We can keep a number or a string if that is all we need. 

What does useState return?

It returns two variables in the array [name, setName]  

where “name” is the state variable and it could be anything, and setName is the function call (can be named anything), which updates the state by providing a new state. 

If you are not familiar with the above syntax, please read array destructuring in JavaScript

In our example we have declared a state variable called name and set it to Steve Marley. React will remember its current value between re-renders and provide the most recent one to our function. If we want to update the current name, we can call setName. 

This is a way to “preserve” some values between the function calls so in other words useState is a new way to use the exact same capabilities that this.state provides in a class. Normally, variables “disappear” when the function exits but state variables are preserved by React. 

It is worth noticing that now our component (functional component) looks pretty simple, crisp and it does not have the level of complexity that a class component normally has. 

Effect Hook 

So far, we have seen extracting stateful logic with the help of hooks and defining/setting states inside a component. But what about managing the DOM from one component to another? Or fetching the data through an API? Or handling Events? All these operations which are quite familiar to usare effects!  

The Effect Hook adds the ability to perform side effects from a functional component. It is a lifecycle Hook that combinescomponentDidMount, componentDidUpdate, and componentWillUnmount in React classes but unified them into a single API. 

useEffect(() => { 
// Do some task here 
}); 

By calling this hook, we are simply telling our component to perform some tasks after render like Data fetching, setting up a subscription, and manually changing the DOM in our React components. 

Let us understand this with an example: 

import React, { useState, useEffect } from"react";
exportdefaultfunctionGetData() { 
const [myData, setData] =useState([]); 
useEffect(() => { 
fetch("https://jsonplaceholder.typicode.com/todos/1") 
.then(response=>response.json()) 
.then(myData=>setData(myData)); 
   }); 
retu
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Easier Angular JS Routing With Angular UI Router

Takeaways from this article In this post, we will understand how and why Angular JS Routing is better in comparison to traditional frameworks, and how this routing can be achieved seamlessly with the help of Angular UI Router.  We will understand the usage and importance of states, and how they help in navigating easily through the application. We will see a sample with a state definition and its usage, and how it helps in resolving issues and making the page user-friendly.  Introduction  Angular JS is a popular application framework that is used for front-end development. It works great when creating single page applications. It is written in JavaScript and is being maintained by tech-giant Google. It is used to interpret the HTML attributes in a webpage in the form of directives and bind the respective input and output components of the model, that are represented in the form of JavaScript variables. Angular UI Routing helps navigate between views and pages seamlessly without getting messy, and in a user-friendly manner.  Note: It is assumed that the reader is aware of technologies like HTML, CSS, JavaScript and Angular JS. Native Angular Routing doesn’t have the following facilities: No nested views No named views Data can’t be passed around between two views The syntax of the route should be literally remembered to navigate the page The URL string has to be manually changed via the code base when a URL is changed. When a URL changes, all the links associated with that URL have to be changed and updated to point to the new location.  In order to minimize the above disadvantages, Angular UI Router is used.  Introduction to Angular JS Routing Angular JS Routing is an advanced technique that helps in routing, that has a declarative approach in navigating through the pages of a website. 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Why You Should Use Angular JS

Takeaways from this articleIn this post, we will understand the prominence of Angular JS and how it plays an important role in front-end web development.  We will understand the applications of Angular JS, along with its usage.  We will also see how it works in comparison to other frameworks that are used for the same purpose.  What is Angular JS Angular JS is a JavaScript framework, that is currently being maintained by tech giant Google. It is used to build single page applications and web-based mobile applications that have interactivity with the users. It is simply an extension of the DOM model, making the application more user-friendly and robust. It is also an MVC framework implementation.  What are the applications of Angular JS? Menu creation Menu is trivial in almost all websites, be it single page, or multi-page. A menu is a navigation tool that responds to an input sent by a user- this could be a click, or a touch. 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This is a convenient way since it helps integrate the view with the website design. This will eliminate the complexity and messiness of the code.  POJO POJO simply means Plain Old JavaScript Object, which indicates that the Angular JS’s data models are simple, plain, easy to understand as well as implement. This also means that functions such as ‘getters’ and ‘setters’ are not required. The characteristics of the application can be changed directly. The presence of directives and DOM elements can be conveniently used to add the required functionalities.  Writing messy code is avoided The need to write too many lines of messy code can be avoided while using Angular JS. The need to write code for MVC pipeline is eliminated, thereby reducing considerable amount of overhead. The data model can be specified without the need to use other extra features or embedding other features. The concept of data binding makes sure that new data is not added into the view portion manually. It has to be integrated into the view with the help of DOM and directives. This way, the entire procedure is simple and easy.  Directives are different, and they are not a part of the code base of the application. This means a directive can be written in parallel without worrying about integrating it with other parts of the code, since this part will be taken care of by Angular JS itself. The time saved can be productively used to improve the quality and features of the Angular JS application instead of worrying about integrating the code with other parts of the application. As a result, there is more flexibility and the ability to extend the code when trying to build high-end web-based applications.  Filters in the data As the name suggests, it is a method that is used to filter the data before it reaches the view part of the application. It helps add filters such as formatting to decimal places, filtering an array based on a specific parameter, reversing the order of ranges, or implementing the concept of pagination for web pages in the application.  Filters can be created to make sure that the functions work properly and have been separated from the application. It also ensures that the functions are only associated with the data transformations with respect to the data and not the entire code of the application itself.  Communications know the context The Publisher-Subscriber system, which is also known as PubSub system is a common model that is used for a separate communication system. Most of the tools that implement Publisher-Subscriber model over the internet wouldn’t be aware of the context in which they are being used. But it is important to ensure that MVC elements that are not related to the same context are not placed together. When Angular JS is combined with Publisher Subscriber model, the context can be specifically mentioned, thereby addressing a specific part of the application. This ensures that the MVC part remains aloof. The remaining parts of the application won’t receive this context/message which means there won’t be any communication. This is easy to implement and simple to use with respect to communication that happens between controllers. Data binding is a technique that helps in the synchronization of the model and the view of the MVC framework. It helps to change, manipulate and work with the model and the view, and also changes their properties and data. With the help of data binding, any changes in the model would be directly reflected in the ‘view’ portion of the framework without the requirement to manipulate DOM or event handlers.  Service providers The scope of the code can be manipulated with the help of controllers in Angular JS. This means data can be placed prior to the code that would be used to implement the business logic or the server code. Controllers perform most of the heavy lifting, since Angular binds specific services to them. This way, the specific service of one controller wouldn’t get mixed with other parts of the application or with the MVC. An API is created to expose the functionality that needs to be used. The offline data can also be managed by synchronizing it with the server, and using various methods to pull or push data to and from a server. It can also be used to create a data sharing resource service that will ensure that different controllers share the same resources at that particular point in time.  Unit Testing capabilities  Angular JS was built by keeping the testing requirements in mind. This is because testing plays an important role, and can prove to be a significant step in identifying loopholes and issues. It also helps understand the overall application from a different perspective. For this change in perspective, end-to-end testing is performed on the Angular JS application. In Angular JS, unit testing can be performed with or without the help of Karma framework. Unit testing is usually performed separately on controllers and directives of Angular JS. The Angular JS application can also be tested by setting up individual test pages that would help create a specific component of the application, and then adding interactivity to it and checking if it works fine or not.  Dependency Injection (DI) The Angular JS application is bound with the help of Dependency Injection (DI). This is because Angular JS contains a built-in DI system. DI is basically a design pattern that discusses the components and their dependencies. DI helps the developers in creating components, working on their dependencies and facilitating the developers with the components that are required. It ensures that controllers are managed within their respective scopes easily. This is because the controllers depend on DI for data to be passed on to it. Why Angular JS should be used Angular JS is an open source framework that binds the data in two ways- the view and the model of the application are synchronized with each other when a user interaction takes place via the interface. This happens automatically so that the DOM gets updated accordingly. It is considered to be budget-friendly, and easy to create.  The highlight of using Angular JS is the fact that MVC is implemented by splitting up the application into parts of MVC that automatically perform the remaining work respectively. The MVC elements are managed by Angular JS without explicitly specifying, and acts as a pipeline that integrates their separate elements. It is an intermediate point of contact that makes sure that the components fit and integrate properly. Adding new functionalities isn’t a difficult task anymore; the view is not a part of DOM, which means new functions can be added and can be integrated with the application by making sure DOM interacts with the directive and the HTML page.  Conclusion In this post, we understood the significance of using AngularJS, how it can be applied in the real-world, and how it is advantageous in comparison to other frameworks with respect to its implementation, DOM model, simple coding capabilities, unit testing abilities and much more. Angular JS applications are simple to build, easy to use (user-friendly) as well as maintain. Since the amount of code that needs to be written is less, the developer can concentrate on building better and more interactive applications thereby improving consumer experience.  
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Why You Should Use Angular JS

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What Is Dependency Injection in AngularJS

AngularJS is an open source JavaScript MVW (Model View Whatever) framework backed by Google and is widely popular for creating dynamic apps. It offers a suite of tools that can be used for building the framework most suited to your single page application development. However, it can also be fully utilized to work for other categories of web pages. It works well with other web-based libraries and is fully extensible. All its features can be modified and even can be replaced to suit your unique development workflow and web feature needs.    As AngularJS is a pure JavaScript framework, it can be added to an HTML page with a normal  tag with src attribute pointing to the source framework library, just like other JavaScript libraries.  AngularJS extends HTML attributes using Directives.  It binds data to HTML using Expressions. AngularJS can be downloaded from https://angularjs.org/. If you’re new to AngularJS, it is better to get introductory information from http://angularjs.org. This site provides the basic information required to start working with AngularJS. It has various features including MVC Architecture, Directives, Expressions, Controllers, Filters, HTML DOM, Modules, Views, AJAX, Scopes, Services, Dependency Injection, and Internationalization. We will deal with Dependency Injection in the following section. IntroductionDependency Injection − AngularJS has a built-in dependency injection (DI) subsystem library whose work is to help the development team by making the application easier to develop, test, and understand. We will learn about each part of DI in detail. The topics we will go through in this article are: Dependency injection in AngularJS Value Injecting a Value Factory Injecting Values into a Factory Service Injecting Values into a Service Providers Configuring a Provider Constants Dependencies Between Modules Dependency injection in AngularJs Today’s software is totally designed in accordance with various design patterns. One such pattern is Dependency Injection. The DI design pattern specifies the pattern in which components are provided with their dependencies, instead of hard coding them within the component. AngularJS comes with a built-in dependency injection mechanism that enables you to divide your application into various types of components which can be injected into each other as their respective dependencies. Modularization of your application makes it easier to use, reuse, configure and even test the different components in your application. According to DI the core types of objects and components include the following: Value Factory Service Provider Constant These are the objects and components which can be injected into each other using AngularJS Dependency Injection. ValueFor AngularJS, the “Value” is a simple object. It can be a number, a string or a POJO (Plain old JavaScript object). This object is used to pass values in AngularJS factories, AngularJS services or AngularJS controllers during the run and config phase. The following example shows the steps involved in using a value. Step 1:  Define a module   var myMod = angular.module("myModule", []); Here, myModule is created using the AngularJS function angular.module(). You can add value, controllers, directives, filters, and more, to your AngularJS application using a module. Step 2: Create a value object and pass data to it.    myMod.value("numberValue", 10);    myMod.value("stringValue", "aaa");    myMod.value("objectValue", { field1 : 123, field2 : "abc"} );  Here, values are defined using the value () function on the module as created in step 1. The first parameter specifies the name of the value, and the second parameter is the value itself passed to other parts of the application. Factories, services and controllers can now reference these values by their value name. Step 3: Injecting a value in Controller function To inject a value into AngularJS controller function, we need to add a parameter with the same value name as that with which the value was defined. Note that the controller function is registered in angular via the angular.module(...).controller(...) function call. The $scope parameter passed to the controller function is the model for the controller. Thus, here myMod is the module registering the controller as myController, and $scope is the model for myController.  var myMod = angular.module("myModule", []);    myMod.value("numberValue", 10);    myMod.controller("myController", function($scope, numberValue) {     console.log(numberValue);    });Example: Using Value in AngularJS: Consider that you have already downloaded the latest AngularJS file from https://angularjs.org/ (here we are using the minified version of AngularJS as angular.min.js). We can even use the AngularJs CDN for the same provided by Google.          Value in AngularJS             Value Example     The numberValue is: {{nValue}}        var myMod = angular.module('myModule', []);  myMod.value("numberValue", 5);  myMod.controller('myController', function($scope, numberValue)   {  $scope.nValue =numberValue;  });       Output: Factory In AngularJS, a factory is a function that is used to return a value. This function creates the value on demand whenever a service or controller needs any value injected from the factory. AngularJS applications normally use a factory function to calculate and return a value. The following example shows the steps involved in using a Factory. Step 1:  Define a module   var myMod = angular.module("myModule", []);   Here, myModule is created using the AngularJS function angular.module(). You can add factory, value, controllers, directives, filters, and more, to your AngularJS application using a module. Step 2: Create a factory object and return data from it.    myMod.factory("myFactory", function() {        return "a value";    }); Here, we have used the factory function to create a Factory named myFactory. This Factory is returning “a value” from it. Step 3: Injecting values into factory Create a controller which gets the factory created value injected (for explanation of Controller, go to the Value part of the article and navigate to its Step 3). To inject a factory value into AngularJS controller function, we need to add a parameter with the same value name as that with which the factory was defined.  var myMod = angular.module("myModule", []);    myMod.factory("myFactory", function() {        return "a value";    });  myMod.controller("MyController", function($scope, myFactory) {    console.log(myFactory);    }); Note: It is not the factory function that is injected, but the value produced by the factory function that gets injected. Example: Using Factory in AngularJS:         Factory                Factory Example    The numberFactory is: {{nFactory}}        var myMod = angular.module('myModule', []);  myMod.factory("myFactory", function() {    return "a value";    });        myMod.controller('myController', function($scope, myFactory) {  $scope. nFactory =myFactory;  });       Output: Service Web Services are helpful functions that perform a task. Similarly, in AngularJS, Service is a JavaScript object which contains a set of functions to perform certain tasks. Services are created by using service() function on a module and then injecting it into controllers. The following example shows the steps involved in using a Service. Step 1:  Define a module   var myMod = angular.module("myModule", []);   Here, myModule is created using the AngularJS function angular.module(). You can add Services, factory, value, controllers, directives, filters, and more, to your AngularJS application using a module. Step 2: Create a service for defining the MathService for calculating basic math functions like add, subtract, multiply and divide. And then create another service, myService for defining a cube method to return the cube of a given number: myMod.service('MathService', function() {      this.add = function(a, b) { return a + b };      this.subtract = function(a, b) { return a - b };      this.multiply = function(a, b) { return a * b };      this.divide = function(a, b) { return a / b };  });  myMod.service('myService', function(MathService){       this.cube = function(a) {          return MathService.multiply(a,MathService.multiply(a,a));        }    }); The above code snippet uses MathService to call multiply function that takes two parameters and calculates the product.  Step 3: Inject the service "myService" into the controller   Create a controller which gets the Service injected (for explanation of Controller, go to the Value part of the article and navigate to its Step 3). To inject a Service function into AngularJS controller function, we need to add a parameter with the same value name as that with which the Service was defined.  myMod.controller('myController', function($scope, myService) {        $scope.doCube = function() {          $scope.result = myService.cube($scope.number);       }    }); Here we can even make it event based by adding an event in the main HTML content as:   Enter a number:            Cube      Result of Service: {{result}}      Example: Using Service in AngularJS:         Service Example           Service Example        Result of Service: {{result}}          var myMod = angular.module("myModule", []);  myMod.service('myService', function(){  this.sum = function(a,b) {  return a + b;  }      });  myMod.controller('myController', function($scope, myService) {  $scope.result = myService.sum (5, 6);  });       Output: Provider In AngularJS, a provider is used to internally create other values or services or factory during config phase (the phase during which AngularJS bootstraps itself). Provider can be considered to be the most flexible form of factory you can create. Provider is a special factory method with a get() function which is used to return the value or service or factory. The following example shows the steps involved in using a Provider. Step 1:  Define a module   var myMod = angular.module("myModule", []);   Here, myModule is created using the AngularJS function angular.module(). You can add Services, factory, value, controllers, directives, filters, and more, to your AngularJS application using a module. Step 2: Create a service using provider which defines a method square to return the square of a number.  We use provider method to create a Provider.   myMod.config(function($provide) {       $provide.provider('myServiceProvider', function() {          this.$get = function() {             var factory = {};               factory.multiply = function(a, b) {                return a * b;              }             return factory;          };       });    });  Step 3: Inject the Provider "myServiceProvider" into the controller   Create a controller which gets the Provider injected (To understand how to create a Controller, go to the Value part of the article and navigate to its Step 3). To inject a Provider function into AngularJS controller function, we need to add a parameter with the same value name as that with which the provider was defined.  myMod.controller('myController', function($scope, myServiceProvider, defaultInput) {        $scope.number = defaultInput;        $scope.result = myServiceProvider.multiply($scope.number, $scope.number);        $scope.square = function() {               $scope.result = myServiceProvider.multiply($scope.number, $scope.number);         }       });   Example: Using Provider in AngularJS:             Provider               Provider Example                        Enter a number:      X 2              Result: {{result}}                                  var myMod  = angular.module("myModule", []);              myMod.config(function($provide) {    $provide.provider('myServiceProvider', function() {    this.$get = function() {    var factory = {};    factory.multiply = function(a) {     return a * a;          }  return factory;      };        });      });             myMod.value("defaultInput", 10);             myMod.controller('myController', function($scope, myServiceProvider, defaultInput) {                $scope.number = defaultInput;                $scope.result = myServiceProvider.multiply($scope.number);    $scope.square = function() {    $scope.result = myServiceProvider.multiply($scope.number);     }        });               Output: Constants Config Phase of AngularJS has some restrictions for injected values, as you cannot inject values into the module.config() function. Instead constants are used to pass values at config phase. To define a constant value we use the constant() function of the defined module. Then for the constant parameter we provide a constant value. The following example shows the steps involved in using a Constant in AngularJS. Step 1: Define a module   var myMod = angular.module("myModule", []);  Here, myModule is created using the AngularJS function angular.module(). You can add Services, factory, value, controllers, directives, filters, and more, to your AngularJS application using a module. Step 2: Create a constant using the constant function and pass constant data to it.      myMod.constant("configParam", "constant value");    Example: Using Constant in AngularJS:              Constant            Constant Example      The numberConstant is:  {{nConstant}}            var myMod = angular.module('myModule', []);      myMod.constant("nConst", 5);      myMod.controller('myController', function($scope,nConst) {  $scope.nConstant =nConst;  });        Output: Difference between Constant and Value Values and Constants seem to be applied in the same way; however, Value differs from Constant in that value cannot be injected into configurations, but it can be intercepted by decorators. Also, a Constant can be used during the apps config phase, whereas a Value is only available during the run phase. The main difference between value and constant is that a value specified using Constant is available during the configuration phase while value specified using Value is available during the run phase. Example showing the difference between a Constant and a Value:          Constant                  Constant Example    {{ID}}          var myMod = angular.module('myModule', []);  myMod.value("myValue", "First Assignment");  myMod.value("myValue", "Second  Assignment");  myMod.constant("myConstant", "First Assignment");  myMod.constant("myConstant", "Second Assignment");  myMod.controller("myController", function($scope, myValue, myConstant) {  console.log("myValue: " + myValue);  console.log("myConstant: " + myConstant);  $scope.ID = " myValue: " + myValue + "&nbsp   myConstant: " + myConstant;  });       Output: Constant Example myValue: Second Assignment myConstant: First Assignment  Complete Example: AngularJS Dependency Injection Let's take an example to deploy all the above mentioned directives.                AngularJS Dependency Injection                 AngularJS Application Showing Dependency Injection         Enter a number:         X  2                Result: {{result}}                          var myMod = angular.module("myMod", []);    myMod.config(function($provide) {    $provide.provider('MathService', function() {    this.$get = function() {    var factory = {};    factory.multiply = function(a, b) {    return a * b;          }    return factory;      };        });      });    myMod.value("defaultInput", 10);    myMod.factory('MathService', function() {                var factory = {};                factory.multiply = function(a, b) {    return a * b;  }    return factory;  });           myMod.service('CalcService', function(MathService){    this.square = function(a) {    return MathService.multiply(a,a);     }         });    myMod.controller('myController', function($scope, CalcService, defaultInput) {    $scope.number = defaultInput;    $scope.result = CalcService.square($scope.number);    $scope.square = function() {    $scope.result = CalcService.square($scope.number);      }        });               Output: ConclusionIn the above article we learned about the Dependency Injection in AngularJS. Dependency Injection is a software design pattern that specifies how components get hold of their dependencies. In this pattern, components are given their dependencies instead of coding them directly within the component. We learned about core types of objects and components like Value, Factory, Service, Provider, and Constant. We learned how to create and register an injectable service and configure an injector with a service provider. We learned how to work with Injecting services to a controller. In the end we summarized with a complete example how Providers, Services, Factory and Value can be used.  
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What Is Dependency Injection in AngularJS

AngularJS is an open source JavaScript MVW (M... Read More