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What is the Use of Axios in React?

While dealing with web applications in React, the most common task is to communicate with backend servers. This is usually done via HTTP protocol.  We are all quite familiar with the very common XML Http Request interface and Fetch API, which allows us to fetch data and make HTTP requests. There is another way to communicate with the backend in React, and in this article we will learn about the awesome library known as Axios and some of the key features of Axios  that have contributed to its popularity among frontend developers. So let’s get started.What is Axios? (A little bit of history) Axios is used to communicate with the backend and it also supports the Promise API that is native to JS ES6.  It is a library which is used to make requests to an API, return data from the API, and then do things with that data in our React application. Axios is a very popular (over 78k stars on Github) HTTP client, which allows us to make HTTP  requests from the browser. Why Do We Need Axios in React? Axios allows us to communicate with APIs easily in our React apps. Though this can also be achieved by other methods like fetch or AJAX, Axios can provide a little more functionality that goes a long way with applications that use React.  Axios is a promise-based library used with Node.js and your browser to make asynchronous JavaScript HTTP requests. When we know we need to implement some promise-based asynchronous HTTP requests in our application, with JavaScript, we usually think of only jQuery’s AJAX or fetch method to get the job done. And while doing so, we are actually going against React!! Did you notice that? So, while React doesn’t care about DOM manipulation at all, why do we need jQuery for our React app? Since React is handling each and everything within its own virtual DOM, perhaps we don’t need  jQuery at all. And hence, Axios becomes a lighter-weight/optimized solution to play around with our HTTP requests. Apart from the above mentioned points, why I personally like AXIOS is because it has a very clean and precise syntax. See  the example code below: Don't worry if you are not familiar with the code, we will learn that later. Using FETCH API:   const getPostsData = () => {   fetch(‘https://jsonplaceholder.typicode.com/posts’)   .then(response => response.json())   .then(data => console.log(data))   .catch(error => console.log(error));   } }  getPostsData();Using AXIOS: const getPostsData = () => {   axios   .get("https://jsonplaceholder.typicode.com/posts")   .then(data => console.log(data.data))   .catch(error => console.log(error));   };  getPostsData();You might be thinking that there isn’t a very big difference but if we consider a POST or Delete or PUT request you can start observing the benefits of using Axios.  Prerequisites In order to use Axios with React, you’ll need the following: Install Node (v 10.7 or above). And if it is already installed, check the version by using npm -v  A React project setup with Create React App or any React boilerplate If you want to learn more about Axios library, head up to this link.  Okay, now that we have spent a good amount of time in understanding Axios, let’s turn our attention on how to use Axios with React. Installing Axios In order to use Axios with React, we need to install Axios. It does not come as a native JavaScript API, so that's why we have to manually import into our project. There are many ways to install Axios. You can pick any of them based on your system environment. Open up a new terminal window, move to your project’s root directory, and run any of the following commands to add Axios to your project. Using npm: $ npm install axios  Using bower package manager: $ bower install axios  Using yarn:  $ yarn add axios  Using unpkg CDN:   <script src="https://unpkg.com/axios/dist/axios.min.js"></script>  Using jsDelivr CDN:    <script src="https://cdn.jsdelivr.net/npm/axios/dist/axios.min.js"></script>  It’s not as complicated as you  might think it’d be.  Fetching and Consuming Data with a Axios (GET-POST-DELETE) Web Applications use HTTP requests, for example, GET, POST and PUT, to communicate with APIs. Axios makes our life simple as it is easy for us now to perform these commands. In this section, we will learn how to use the Axios to make REST API calls like GET, POST  and DELETE in React App. So let’s get started. Performing GET Request with Axios Let’s create a new component named My List and hook it into the component DidMount lifecycle as shown below. After that we will fetch data with Get request by importing axios. Here we are using JSON placeholder API for fetching the dummy list data of users. import React from 'react';  import axios from 'axios';  export default class MyList extends React.Component {   state = {   persons: []   }  componentDidMount() {   axios.get(`https://jsonplaceholder.typicode.com/users`)   .then(response => { const users = response.data;   this.setState ({users});   })   }  render() {   return (   < ul >   {this.state.users.map (user => {user.name} )}   < /ul >   )   }  }In the above component named MyList, we have imported Axios first. axios.get(--URL--) is used to get a promise which will return a response object. The received data in response.data is assigned to the user's object.  We can also retrieve other Information like status code and others received with the response. Performing POST Request with Axios Now let’s create another component named AddUser for using the POST request which will add a user in the user list. (a.ka. Adding data into database) import React from 'react'; import axios from 'axios'; export default class AddUser extends React.Component {  state = {  userName: '',  }  handleChange = event => {  this.setState({ userName: event.target.value });  }  handleSubmit = event => {  event.preventDefault();  const user = {  userName: this.state.userName  };  axios.post(`https://jsonplaceholder.typicode.com/users`, { user })  .then(res => {  console.log(res);  console.log(res.data);  })[Text Wrapping Break] }  render() {  return (  <div>  <form onSubmit={this.handleSubmit}>  <label>  User Name:  <input type="text" name="name" onChange={this.handleChange}/>  </label>  <button type="submit">Add</button>  </form>  </div>  )  }  }In the above example, we have made a HTTP Post request to modify the database, which is a user list and added a new user to the database. Because we've initialized the state, in handleChange() we have updated the state when the API request returns data successfully. Performing POST Request with Axios Finally, the delete method. axios.delete is used to make a Delete request to the server. axiox.delete accepts two parameters: url and optional config.  axios.delete(url, { data: { foo: "bar" }, headers: { "Authorization": "***" } }); We can use config.data to set the request body and headers as shown in the below snippet. Consider the same component as above and modify the request as follows: handleSubmit = event => {   event.preventDefault();   axios.delete(`https://jsonplaceholder.typicode.com/users/${this.state.userName}`)   .then(res => {   console.log(res);   console.log(res.data);   })  } And you are done! — you’ve got a transformed and simplified React appSending custom headers with Axios Sending custom headers with Axios is very simple and straightforward.  It is done by passing an object containing the headers as the last argument.  See the below code reference:  const options = {   headers: {'X-Custom-Header': 'value'}  };  axios.post('/save', { a: 50 }, options);Looking at the response object When we send a request to server and it is successful, our then() callback will receive a response object which can have the following properties: data: It is the payload returned from the server. By default, Axios expects JSON and will parse this back into a JavaScript object for you. status: It is basically the HTTP code returned from the server. statusText: it refers to the HTTP status message returned by the server. headers: It contains all the headers sent back by the server. config: It has the original request configuration. request: It is the actual XMLHttpRequest object (when it is running in a browser)Looking at the error object And if there’s a problem with the request, the promise will be rejected with an error object containing at least one or few of the following properties: message: the error message text. response: the response object (if received) as described in the previous section. request: the actual XMLHttpRequest object (when running in a browser). config: the original request configuration. Features of Axios Library as per the Documentation: Automatically transforms for JSON data Axios is intelligent because it automatically converts a response to JSON, so while using Axios we usually skip the step of converting the response to JSON, unlike we do in Fetch() Transform request and response data Make HTTP requests from Node.js Make XMLHttpRequests from the browser Client-side support for protecting against XSRF Supports the Promise API Intercept request and response: HTTP interceptors are used when we need to change HTTP requests from our application to the server. Axios provides a way to intercept HTTP requests.  And hence Interceptors provide us the ability to do that without writing any extra code. Has an ability to cancel requests It has a built-in feature that provides client-side protection against cross-site request forgery. In case you want to dig in and learn more about these features, head up to the official documentation of AXIOS. MAKING MULTIPLE REQUESTS WITH AXIOS With Axios we get an ability to make multiple HTTP requests and handle them simultaneously using the axios.all() method. This method takes in an array of arguments and in return we get a single promise object that only resolves when all the arguments passed in the array have been resolved. Look at the below example, where we are making multiple requests to the GitHub api using the axios.all() method. axios.all([   axios.get('https://api.github.com/users/defunkt),   axios.get('https://api.github.com/users/evanphx)  ])  .then(response => {   console.log('Date created: ', response[0].data.created_at);   console.log('Date created: ', response[1].data.created_at);  }); What will happen in the above code is that it will make simultaneous requests to an array of arguments in parallel, return the response data and will console the created_at object from each of the API responses.  Think About Abstraction  In Axios it’s quite possible to create a base instance where we can drop the URL for our API as shown below:   const api = axios.create({ baseURL: "https://api.github.com/users/evanphx" });And then simply abstract the URL like shown:  async getPostsData() { const response = await api.get();   try {   this.setState({   posts: response.data.posts,   isLoading: false   });   } catch (error) {   this.setState({ error, isLoading: false });   }  }Shorthand Methods in Axios  You have already seen that Axios provides an easy-to-use API contract model in a compact package for most of our HTTP communication needs. Do you know that Axios has some shorthand methods for performing different HTTP requests?  Check them below:  axios.request(config) axios.get(url[, config]) axios.delete(url[, config]) axios.head(url[, config]) axios.options(url[, config]) axios.post(url[, data[, config]]) axios.put(url[, data[, config]]) axios.patch(url[, data[, config]]) Some Awesome Facts about Axios  Wondering about some cool facts about Axios? Let’s check them out! For Axios, there is no need for a browser environment. This neat simple library also works on the server-side!  And hence we can use Axios in our Node applications as well. Apart from fetching or retrieving data, with the help of Axios we can also check the token expiry while requesting data for client-side and server-side. And when the token is already expired we can call an API to get the new token and continue the previous API request.  In Axios, monitoring the upload and download progress is quite simple. How? Just set a callback in the request config as shown below, and enjoy. axios({   method: "get",   url: "/myFilePath",   responseType: "blob",   onDownloadProgress: (progressEvent) => { const percentCompleted = Math.round(   (progressEvent.loaded * 100) / progressEvent.total   );  console.log(percentCompleted)   this.setState({   loadingPercent: percentCompleted,   });   },  }).then((response) => {   alert("We are Ready!");  });ConclusionI hope this article has helped you in understanding about Axios and its usage for various features like fetching or retrieving data and handling responses.  In this article, we saw several practical examples to check the power of Axios inside a React application to create HTTP requests and handle responses. We also got an idea about why it is a better approach than a normal fetch api.  So what are you waiting for? Go ahead and give Axios a try. It will definitely make your life easier. Happy Learning.

What is the Use of Axios in React?

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What is the Use of Axios in React?

While dealing with web applications in React, the most common task is to communicate with backend servers. This is usually done via HTTP protocol.  

We are all quite familiar with the very common XML Http Request interface and Fetch API, which allows us to fetch data and make HTTP requests. 

There is another way to communicate with the backend in React, and in this article we will learn about the awesome library known as Axios and some of the key features of Axios  that have contributed to its popularity among frontend developers. 

So let’s get started.

What is Axios? (A little bit of history) 

  • Axios is used to communicate with the backend and it also supports the Promise API that is native to JS ES6.  
  • It is a library which is used to make requests to an API, return data from the API, and then do things with that data in our React application. 
  • Axios is a very popular (over 78k stars on Github) HTTP client, which allows us to make HTTP  requests from the browser. 

Why Do We Need Axios in React? 

Axios allows us to communicate with APIs easily in our React apps. Though this can also be achieved by other methods like fetch or AJAX, Axios can provide a little more functionality that goes a long way with applications that use React.  

Axios is a promise-based library used with Node.js and your browser to make asynchronous JavaScript HTTP requests. 

When we know we need to implement some promise-based asynchronous HTTP requests in our application, with JavaScript, we usually think of only jQuery’s AJAX or fetch method to get the job done. And while doing so, we are actually going against React!! Did you notice that? 

  • So, while React doesn’t care about DOM manipulation at all, why do we need jQuery for our React app? 
  • Since React is handling each and everything within its own virtual DOM, perhaps we don’t need  jQuery at all. 
  • And hence, Axios becomes a lighter-weight/optimized solution to play around with our HTTP requests. 
  • Apart from the above mentioned points, why I personally like AXIOS is because it has a very clean and precise syntax. See  the example code below: 
  • Don't worry if you are not familiar with the code, we will learn that later. 

Using FETCH API:   

const getPostsData = () => {
  fetch(‘https://jsonplaceholder.typicode.com/posts’)
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.log(error));
  }
}
 getPostsData();

Using AXIOS: 

const getPostsData = () => {
  axios
  .get("https://jsonplaceholder.typicode.com/posts")
  .then(data => console.log(data.data))
  .catch(error => console.log(error));
  };
 getPostsData();

You might be thinking that there isn’t a very big difference but if we consider a POST or Delete or PUT request you can start observing the benefits of using Axios.  

Prerequisites 

In order to use Axios with React, you’ll need the following: 

  1. Install Node (v 10.7 or above). 

And if it is already installed, check the version by using 

npm -v  
  1. A React project setup with Create React App or any React boilerplate 

If you want to learn more about Axios library, head up to this link.  

Okay, now that we have spent a good amount of time in understanding Axios, let’s turn our attention on how to use Axios with React. 

Installing Axios 

In order to use Axios with React, we need to install Axios. It does not come as a native JavaScript API, so that's why we have to manually import into our project. 

There are many ways to install Axios. You can pick any of them based on your system environment. 

Open up a new terminal window, move to your project’s root directory, and run any of the following commands to add Axios to your project. 

Using npm: 

$ npm install axios  

Using bower package manager: 

$ bower install axios  

Using yarn:  

$ yarn add axios  

Using unpkg CDN:   

<script src="https://unpkg.com/axios/dist/axios.min.js"></script>  

Using jsDelivr CDN:    

<script src="https://cdn.jsdelivr.net/npm/axios/dist/axios.min.js"></script>  

It’s not as complicated as you  might think it’d be.  

Fetching and Consuming Data with a Axios (GET-POST-DELETE) 

Web Applications use HTTP requests, for example, GET, POST and PUT, to communicate with APIs. Axios makes our life simple as it is easy for us now to perform these commands. 

In this section, we will learn how to use the Axios to make REST API calls like GET, POST  and DELETE in React App. So let’s get started. 

Performing GET Request with Axios 

Let’s create a new component named My List and hook it into the component DidMount lifecycle as shown below. After that we will fetch data with Get request by importing axios. 

Here we are using JSON placeholder API for fetching the dummy list data of users. 

import React from 'react';
 import axios from 'axios';
 export default class MyList extends React.Component {
  state = {
  persons: []
  }
 componentDidMount() {
  axios.get(`https://jsonplaceholder.typicode.com/users`)
  .then(response => {
const users = response.data;
  this.setState ({users});
  })
  }
 render() {
  return (
  < ul >
  {this.state.users.map (user =>  {user.name}   )}
  < /ul >
  )
  }
 }

In the above component named MyList, we have imported Axios first. axios.get(--URL--) is used to get a promise which will return a response object. The received data in response.data is assigned to the user's object.  

We can also retrieve other Information like status code and others received with the response. 

Performing POST Request with Axios 

Now let’s create another component named AddUser for using the POST request which will add a user in the user list. (a.ka. Adding data into database) 

import React from 'react';
import axios from 'axios';
export default class AddUser extends React.Component {
 state = {
 userName: '',
 }
 handleChange = event => {
 this.setState({ userName: event.target.value });
 }
 handleSubmit = event => {
 event.preventDefault();
 const user = {
 userName: this.state.userName
 };
 axios.post(`https://jsonplaceholder.typicode.com/users`, { user })
 .then(res => {
 console.log(res);
 console.log(res.data);
 })[Text Wrapping Break] }
 render() {
 return (
 <div>
 <form onSubmit={this.handleSubmit}>
 <label>
 User Name:
 <input type="text" name="name" onChange={this.handleChange}/>
 </label>
 <button type="submit">Add</button>
 </form>
 </div>
 )
 }
 }

In the above example, we have made a HTTP Post request to modify the database, which is a user list and added a new user to the database. 

Because we've initialized the state, in handleChange() we have updated the state when the API request returns data successfully. 

Performing POST Request with Axios 

Finally, the delete method. axios.delete is used to make a Delete request to the server. 

axiox.delete accepts two parameters: url and optional config.  

axios.delete(url, { data: { foo: "bar" }, headers: { "Authorization": "***" } }); 

We can use config.data to set the request body and headers as shown in the below snippet. 

Consider the same component as above and modify the request as follows: 

handleSubmit = event => {
  event.preventDefault();
  axios.delete(`https://jsonplaceholder.typicode.com/users/${this.state.userName}`)
  .then(res => {
  console.log(res);
  console.log(res.data);
  })
 } 

And you are done! — you’ve got a transformed and simplified React app

Sending custom headers with Axios 

Sending custom headers with Axios is very simple and straightforward.  

It is done by passing an object containing the headers as the last argument.  

See the below code reference:  

const options = {
  headers: {'X-Custom-Header': 'value'}
 };
 axios.post('/save', { a: 50 }, options);

Looking at the response object 

When we send a request to server and it is successful, our then() callback will receive a response object which can have the following properties: 

  • data: It is the payload returned from the server. By default, Axios expects JSON and will parse this back into a JavaScript object for you. 
  • statusIt is basically the HTTP code returned from the server. 
  • statusText: it refers to the HTTP status message returned by the server. 
  • headers: It contains all the headers sent back by the server. 
  • config: It has the original request configuration. 
  • request: It is the actual XMLHttpRequest object (when it is running in a browser)

Looking at the error object 

And if there’s a problem with the request, the promise will be rejected with an error object containing at least one or few of the following properties: 

  • message: the error message text. 
  • response: the response object (if received) as described in the previous section. 
  • request: the actual XMLHttpRequest object (when running in a browser). 
  • configthe original request configuration. 

Features of Axios Library as per the Documentation: 

  • Automatically transforms for JSON data 

Axios is intelligent because it automatically converts a response to JSON, so while using Axios we usually skip the step of converting the response to JSON, unlike we do in Fetch() 

  • Transform request and response data 
  • Make HTTP requests from Node.js 
  • Make XMLHttpRequests from the browser 
  • Client-side support for protecting against XSRF 
  • Supports the Promise API 
  • Intercept request and response: 

HTTP interceptors are used when we need to change HTTP requests from our application to the server. Axios provides a way to intercept HTTP requests.  And hence Interceptors provide us the ability to do that without writing any extra code. 

  • Has an ability to cancel requests 

It has a built-in feature that provides client-side protection against cross-site request forgery. 

In case you want to dig in and learn more about these features, head up to the official documentation of AXIOS. 

MAKING MULTIPLE REQUESTS WITH AXIOS 

With Axios we get an ability to make multiple HTTP requests and handle them simultaneously using the axios.all() method. This method takes in an array of arguments and in return we get a single promise object that only resolves when all the arguments passed in the array have been resolved. 

Look at the below example, where we are making multiple requests to the GitHub api using the axios.all() method. 

axios.all([
  axios.get('https://api.github.com/users/defunkt),
  axios.get('https://api.github.com/users/evanphx)
 ])
 .then(response => {
  console.log('Date created: ', response[0].data.created_at);
  console.log('Date created: ', response[1].data.created_at);
 }); 

What will happen in the above code is that it will make simultaneous requests to an array of arguments in parallelreturn the response data and will console the created_at object from each of the API responses.  

Think About Abstraction  

In Axios it’s quite possible to create a base instance where we can drop the URL for our API as shown below:   

const api = axios.create({ baseURL: "https://api.github.com/users/evanphx" });

And then simply abstract the URL like shown:  

async getPostsData() {
const response = await api.get();
  try {
  this.setState({
  posts: response.data.posts,
  isLoading: false
  });
  } catch (error) {
  this.setState({ error, isLoading: false });
  }
 }

Shorthand Methods in Axios  

You have already seen that Axios provides an easy-to-use API contract model in a compact package for most of our HTTP communication needs. 

Do you know that Axios has some shorthand methods for performing different HTTP requests?  

Check them below:  

  • axios.request(config) 
  • axios.get(url[, config]) 
  • axios.delete(url[, config]) 
  • axios.head(url[, config]) 
  • axios.options(url[, config]) 
  • axios.post(url[, data[, config]]) 
  • axios.put(url[, data[, config]]) 
  • axios.patch(url[, data[, config]]) 

Some Awesome Facts about Axios  

Wondering about some cool facts about Axios? Let’s check them out! 

  • For Axios, there is no need for a browser environment. This neat simple library also works on the server-side!  And hence we can use Axios in our Node applications as well. 
  • Apart from fetching or retrieving data, with the help of Axios we can also check the token expiry while requesting data for client-side and server-side. And when the token is already expired we can call an API to get the new token and continue the previous API request.  
  • In Axios, monitoring the upload and download progress is quite simple. How? Just set a callback in the request config as shown below, and enjoy. 
axios({
  method: "get",
  url: "/myFilePath",
  responseType: "blob",
  onDownloadProgress: (progressEvent) => {
const percentCompleted = Math.round(
  (progressEvent.loaded * 100) / progressEvent.total
  );
 console.log(percentCompleted)
  this.setState({
  loadingPercent: percentCompleted,
  });
  },
 }).then((response) => {
  alert("We are Ready!");
 });

Conclusion

I hope this article has helped you in understanding about Axios and its usage for various features like fetching or retrieving data and handling responses.  

In this article, we saw several practical examples to check the power of Axios inside a React application to create HTTP requests and handle responses. 

We also got an idea about why it is a better approach than a normal fetch api.  

So what are you waiting for? Go ahead and give Axios a try. It will definitely make your life easier. 

Happy Learning.

KnowledgeHut

KnowledgeHut

Author

KnowledgeHut is an outcome-focused global ed-tech company. We help organizations and professionals unlock excellence through skills development. We offer training solutions under the people and process, data science, full-stack development, cybersecurity, future technologies and digital transformation verticals.
Website : https://www.knowledgehut.com

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Handling React Events - A Detailed Guide

Event handling essentially allows the user to interact with a webpage and do something specific when a certain event like a click or a hover happens. When the user interacts with the application, events are fired, for example, mouseover, key press, change event, and so on. The application must handle events and execute the code. In short, events are the actions to which javascript can respond.   The actions to which javascript can respond are called events. Handling events with react is  very similar to handling events in DOM elements. Below are some general events that you would see in and out when dealing with react based websites:  Clicking an element  Submitting a form Scrolling page Hovering an element  Loading a webpage Input field change User stroking a key Image loading Naming Events in React Handling events with react is very similar to handling events in DOM elements, although there are some syntactic differences.   React events are written in camelCase.   A function is passed as the event handler rather than string. The way to write events in html / DOM is below:        click me onclick is written in lower case in html as shown above and what action to take when this onclick event triggers is taken care of by handleClick.In React, events are named using camel case and you pass a function as event handler as shown below:  Like in a functional component, event is written like below:       click me   In class based component ,event is written like below        click me Defining Events:Events are normally used in combination with functions, and the function is not executed until the event occurs, and the combination of event, HTML element, and javascript function is called binding which means to map all three. Generic syntax is:      Example:  Create a button element and what happens when onClick event triggered is driven by the function which is func() shown below     click me Let’s see some of the event attributes:   onmouseover : The mouse is moved over an element onmouseup : The mouse button is released onmouseout : The mouse  is moved off an element onmousemove: The mouse is moved Onmousedown: mouse button is pressed  onload : A image is done loading onunload: Existing the page  onblur : Losing Focus  on element  onchange : Content of a field changes onclick: Clicking an object  ondblclick: double clicking an object  onfocus element getting a focus  Onkeydown: pushing a keyboard key Onkeyup: keyboard key is released Onkeypress: keyboard key is pressed  Onselect: text is selected These are some examples of events:                                         Events                               function testApp (){                        alert((“Hello Event”);                                                   test Clicked                  test double Clicked                     Synthetic Events When you specify an event in JSX, you are not directly dealing with regular DOM events, you are dealing with a react event type called a synthetic event.It's a simple wrapper for native event instances and every synthetic event created needs to be garbage-collected which can be resource intensive in terms of CPU. The synthetic event object has properties mentioned below:  Boolean isTrusted  DOMEvent nativeEvent number timeStamp   void preventDefault() number eventPhase Synthetic events provide an interface and reduce browser inconsistencies and the event contains required information for its propagation to work. Synthetic event is reused for performance reasons in the browser, A synthetic event is a cross-browser wrapper around the browser’s native event it has the same interface as the native event. Synthetic events are delegated to the document node. Therefore native events are triggered first and the events bubble up to document, after which the synthetic events are triggered. The synthetic event object will be reused and all the properties will be nullified after the event callback has been invoked and this is for performance reasons.The workflow of synthetic event in react is:    Element ---- > Event ---- > synthetic event  ---- > handler(e)                                |                                                      |                                |  _______  Component ________|  umber timeStamp The Basics of React Event Handling Let’s explore how to handle events in react and we will showcase the click event and how it holds good for other types of events. Let’s start with functional components by creating a  file as clickAppHandler.js.In this file let’s create a  functional component  as shown below                        Import React from ‘...react’                         function clickAppHandler() {                                function clickHandler() {                                        console.log(‘clicked’)                                         }                                  return (                                                                                  Click                                                                          )                         }                       export default clickAppHandler  When onClick event triggers clickHandler function is called as shown below and when you click the button console will print the string “clicked” After this you need the add a component in the app component. In our code above you can see on click we pass the function as event handler and you will notice that we haven't added parentheses as it becomes a function, and we do not want that and we want handler to be a function not a function call. When a new component is rendered its event handler functions are added to the mapping maintained by the react.When the event is triggered and it hits and DOM object ,react maps the event to the handler, if it matches it calls the handler. The event handling in react is declarative and the advantage of declarative way to handlers is that they are part of the User interface structure.  Let’s take a look at event handling in class components                       Import React, { Component } from ‘...react’                         class TestApp extends Component {                              clickHandler() {                                  console.log(“clicked”)                                }                                render(){                                      return(                                                                                     Click me                                                                                 )                                 }                            }                       export default TestApp You cannot return false to prevent default behaviour in React. You must call preventDefault explicitly.  In HTML it looks like below:    Click Output: It will print “Clicked”  And in React, like this:  function clickHandle(e) {       e.preventDefault();       console.log(“Handled”);   }  Click  Output : console will print “Handled”  There are some  event handlers triggered by an event in the bubbling phase which is the same as with the normal DOM API; simply attach a handler to an eventual parent of an element and any events triggered on that element will bubble to the parent as long as it's not stopped via stopPropagation along the way   Click me  Below are some of the event handlers triggered in the bubbling phase:  MouseEvents           onClick           onDrag          onDoubleClick Keyboard Events                    onKeyDown                    onKeyPress                    onKeyUp Focus Events                  onFocus   onBlur To capture an event handler for the capture phase, append capture to the event name. For example, instead of using onClick, use onClickCapture to handle the click event.  Capture event example:                  Click me    Additional ExamplesExample1                       Import React from ‘...react’                         function clickAppHandler() {                                function clickHandler() {                                        console.log(‘clicked’)                                         }                                  return (                                                                                  Click                                                                          )                         }                       export default clickAppHandler   Example2       This example is along with HTML in a single file                                                            Events                               function testApp (){                        alert((“Hello Event”);                                                   test Clicked                  test double Clicked                     Adding Events: Below example is how you add an event. Highlighted in bold                      Import React from ‘...react’                         function clickAppHandler() {                                function clickHandler() {                                        console.log(‘clicked’)                                         }                                  return (                                                                                  Click                                                                          )                         }                       export default clickAppHandler  Passing Arguments to Event HandlerThere are two ways arguments are passed to event handler  Arrow function                    this.handleClick(id,e)}>Click                onClick is the event                e is the event object                 id can be state or props or some data Bind method      Click  In this case event object is automatically passed In both methods e represents the react event and its passed after the ID as second argument,With an arrow function this event e is passed explicitly but with bind method its automatically passed.                                     Import React,{ Component } from “react”;                                         class TestApp extends Component {                                           state = {                                                       id: 2,                                                      Name: “TestApp Dummy”                                                };                                                             //arrow function                                                 handleClick = (id,e) => {                                                       console.log(id);                                                       console.log(e);                                                  };                                               handleArg = (e) => { this.handleClick(this.state.id,e);}                                                          render() {     return (                    TestApp,{this.state.name}            onClick={this.handleArg}>Display            );   }  }  The react event is an object and obtained from react. Instead of creating a separate function for passing argument, you can directly pass the anonymous arrow function as shown in the render function below:     render() {        return (                                                                                                       TestApp,{this.state.name}                                                {                           this.handleClick(this.state.id,e);                                                               }}>Display                                                                                                         );                                                 }                                            }    Output:   click on button  “TestApp Dummy “                   Let’s see only how bind method looks like in the render function    render() {                                         return (                                                                                                 TestApp,{this.state.name}                                                   Display                                                                                                       );                                                  }                                              } Output: this will display the h1 tag and when you click the button handleClick function gets invoked and the console will display id of the state object as shown above. Building a Practice to Thoroughly Understand Events This blog focuses on event handling, which in turn teaches about event handlers declared in JSX markup.This approach helps in tracking down the element mapped with events in an easy way.  We also learned how to handle multiple event handlers in a single element by using JSX attributes.we also learned about ways to bind event handler and  parameter values. Then we learned about synthetic events which are abstractions around native events. The best way you can retain this learning is by practicing more and tackling the complexities that may arise as you practice. You can find several tutorials on the internet or share your questions with us here. Happy learning! 
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Handling React Events - A Detailed Guide

Event handling essentially allows the user to inte... Read More

MongoDB Query Document Using Find() With Example

MongoDB's find() method selects documents from a collection or view and returns a cursor to those documents. There are two parameters in this formula: query and projection.Query – This is an optional parameter that specifies the criteria for selection. In simple terms, a query is what you want to search for within a collection.Projection – This is an optional parameter that specifies what should be returned if the query criteria are satisfied. In simple terms, it is a type of decision-making that is based on a set of criteria.MongoDB's Flexible SchemaA NoSQL database, which stands for "not only SQL," is a way of storing and retrieving data that is different from relational databases' traditional table structures (RDBMS).When storing large amounts of unstructured data with changing schemas, NoSQL databases are indeed a better option than RDBMS. Horizontal scaling properties of NoSQL databases allow them to store and process large amounts of data.These are intended for storing, retrieving, and managing document-oriented data, which is frequently stored in JSON format (JavaScript Object Notation). Document databases, unlike RDBMSs, have a flexible schema that is defined by the contents of the documents.MongoDB is one of the most widely used open-source NoSQL document databases. MongoDB is known as a 'schemaless' database because it does not impose a specific structure on documents in a collection.MongoDB is compatible with a number of popular programming languages. It also offers a high level of operational flexibility because it scales well horizontally, allowing data to be spread or 'sharded' across multiple commodity servers with the ability to add more servers as needed. MongoDB can be run on a variety of platforms, including developer laptops, private clouds, and public clouds.Querying documents using find()MongoDB queries are used to retrieve or fetch data from a MongoDB database. When running a query, you can use criteria or conditions to retrieve specific data from the database.The function db.collection is provided by MongoDB. find() is a function that retrieves documents from a MongoDB database.In MongoDB, the find method is used to retrieve a specific document from the MongoDB collection. In Mongo DB, there are a total of six methods for retrieving specific records.find()findAndModify()findOne()findOneAndDelete()findOneAndReplace()findOneAndUpdate()Syntax:find(query, projection)We can fetch a specific record using the Find method, which has two parameters. If these two parameters are omitted, the find method will return all of the documents in the MongoDB collection.Example:Consider an example of employees with the database of employee_id and employee_name and we will fetch the documents using find() method.First, create a database with the name “employees” with the following code:use employeesNow, create a collection “employee” with:db.createCollection("employee")In the next step we will insert the documents in the database:db.employee.insert([{employee_id: 101, employee_name: "Ishan"}, {employee_id: 102, employee_name: "Bhavesh"}, {employee_id: 103, employee_name: "Madan"}])Find all Documents:To get all the records in a collection, we need to use the find method with an empty parameter. In other words, when we need all the records, we will not use any parameters.db.employee.find()Output in Mongo ShellThe pretty() method can be used to display the results in a formatted manner.Syntax:db.COLLECTION_NAME.find().pretty()Let’s check our documents with pretty() method:Query FiltersWe will see examples of query operations using the db.collection.find() method in mongosh.We will use the employee collection in the employees database.db.employee.insert([{employee_id: 101, employee_name: "Ishan", age: 21, email_id: "ishanjain@gmail.com"}, {employee_id: 102, employee_name: "Bhavesh", age: 22, email_id: "bhaveshg@gmail.com"}, {employee_id: 103, employee_name: "Madan", age: 23, email_id: "madan@gmail.com"}])As we have seen earlier that to select all the documents in the database we pass an empty document as the query filter parameter to the find method.db.employee.find().pretty()Find the first document in a collection:db.employee.findOne()Find a document by ID:db.employee.findOne({_id : ObjectId("61d1ae0b56b92c20b423a5a7")})Find Documents that Match Query Criteriadb.employee.find({“age”: “22”})db.employee.find({"employee_name": "Madan"}).pretty()Sort Results by a Field:db.employee.find().sort({age: 1}).pretty()order by age, in ascending orderdb.employee.find().sort({age: -1}).pretty()order by age, in descending orderAND Conditions:A compound query can specify conditions for multiple fields in the documents in a collection. A logical AND conjunction connects the clauses of a compound query indirectly, allowing the query to select all documents in the collection that meet the specified conditions.In the following example, we will consider all the documents in the employee collection where employee_id equals 101 and age equals 21.db.employee.find({"employee_id": 101, "age": "21" }).pretty()Querying nested fieldsThe embedded or nested document feature in MongoDB is a useful feature. Embedded documents, also known as nested documents, are documents that contain other documents.You can simply embed a document inside another document in MongoDB. Documents are defined in the mongo shell using curly braces (), and field-value pairs are contained within these curly braces.Using curly braces, we can now embed or set another document inside these fields, which can include field-value pairs or another sub-document.Syntax:{ field: { field1: value1, field2: value2 } }Example:We have a database “nested” and in this database we have collection “nesteddoc”.The following documents will insert into the nesteddoc collection.db.nesteddoc.insertMany([ { "_id" : 1, "dept" : "A", "item" : { "sku" : "101", "color" : "red" }, "sizes" : [ "S", "M" ] }, { "_id" : 2, "dept" : "A", "item" : { "sku" : "102", "color" : "blue" }, "sizes" : [ "M", "L" ] }, { "_id" : 3, "dept" : "B", "item" : { "sku" : "103", "color" : "blue" }, "sizes" : "S" }, { "_id" : 4, "dept" : "A", "item" : { "sku" : "104", "color" : "black" }, "sizes" : [ "S" ] } ])Place the documents in the collection now. Also, take a look at the results:As a result, the nesteddoc collection contains four documents, each of which contains nested documents. The find() method can be used to access the collection's documents.db.nesteddoc.find()Specify Equality Condition:In this example, we will select the document from the nesteddoc query where dept equals “A”.db.nesteddoc.find({dept: "A"})Querying ArraysUse the query document {: } to specify an equality condition on an array, where is the exact array to match, including the order of the elements.The following query looks for all documents where the field tags value is an array with exactly two elements, "S" and "M," in the order specified:db.nesteddoc.find( { sizes: ["S", "M"] } )Use the $all operator to find an array that contains both the elements "S" and "M," regardless of order or other elements in the array:db.nested.find( { sizes: { $all: ["S", "M"] } } )Query an Array for an Element:The following example queries for all documents where size is an array that contains the string “S” as one of its elements:db.nesteddoc.find( { sizes: "S" } )Filter conditionsTo discuss the filter conditions, we will consider a situation that elaborates this. We will start by creating a collection with the name “products” and then add the documents to it.db.products.insertMany([ { _id: 1, item: { name: "ab", code: "123" }, qty: 15, tags: [ "A", "B", "C" ] }, { _id: 2, item: { name: "cd", code: "123" }, qty: 20, tags: [ "B" ] }, { _id: 3, item: { name: "ij", code: "456" }, qty: 25, tags: [ "A", "B" ] }, { _id: 4, item: { name: "xy", code: "456" }, qty: 30, tags: [ "B", "A" ] }, { _id: 5, item: { name: "mn", code: "000" }, qty: 20, tags: [ [ "A", "B" ], "C" ] }])To check the documents, use db.products.find():$gt$gt selects documents with a field value greater than (or equal to) the specified value.db.products.find( { qty: { $gt: “20” } } )$gte:$gte finds documents in which a field's value is greater than or equal to (i.e. >=) a specified value (e.g. value.)db.products.find( { qty: { $gte: 20 } } )$lt:$lt selects documents whose field value is less than (or equal to) the specified value.db.products.find( { qty: { $lt: 25 } } )$lte:$lte selects documents in which the field's value is less than or equal to (i.e. =) the specified value.db.products.find( { qty: { $lte: 20 } } )Query an Array by Array Length:To find arrays with a specific number of elements, use the $size operator. For example, the following selects documents with two elements in the array.db.products.find( { "tags": {$size: 2} } )ProjectionIn MongoDB, projection refers to selecting only the data that is required rather than the entire document's data. If a document has five fields and you only want to show three of them, select only three of them.The find() method in MongoDB accepts a second optional parameter, which is a list of fields to retrieve, as explained in MongoDB Query Document. When you use the find() method in MongoDB, it displays all of a document's fields. To prevent this, create a list of fields with the values 1 or 0. The value 1 indicates that the field should be visible, while 0 indicates that it should be hidden.Syntax:db.COLLECTION_NAME.find({},{KEY:1})Example:We will consider the previous example of products collection. Run the below command on mongoshell to learn how projection works:db.products.find({},{"tags":1, _id:0})Keep in mind that the _id field is always displayed while executing the find() method; if you do not want this field to be displayed, set it to 0.Optimized FindingsTo retrieve a document from a MongoDB collection, use the Find method.Using the Find method, we can retrieve specific documents as well as the fields that we require. Other find methods can also be used to retrieve specific documents based on our needs.By inserting array elements into the query, we can retrieve specific elements or documents. To retrieve data for array elements from the collection in MongoDB, we can use multiple query operators.
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MongoDB Query Document Using Find() With Example

MongoDB's find() method selects documents from a c... Read More

Implementing MongoDb Map Reduce using Aggregation

Algorithms and applications in today's data-driven market collect data about people, processes, systems, and organisations 24 hours a day, seven days a week, resulting in massive amounts of data. The problem is figuring out how to process this massive amount of data efficiently without sacrificing valuable insights.What is Map Reduce? The MapReduce programming model comes to the rescue here. MapReduce, which was first used by Google to analyse its search results, has grown in popularity due to its ability to split and process terabytes of data in parallel, generating results faster. A (Key,value) pair is the basic unit of information in MapReduce. Before feeding the data to the MapReduce model, all types of structured and unstructured data must be translated to this basic unit. The MapReduce model, as the name implies, consists of two distinct routines: the Map-function and the Reduce-function.  MapReduce is a framework for handling parallelizable problems across huge files using a huge number of devices (nodes), which are collectively referred to as a cluster (if all nodes are on the same local network and use similar hardware) or a grid (if the nodes are shared across geographically and administratively distributed systems, and use more heterogeneous hardware).  When data stored in a filesystem (unstructured) or a database(structured) is processed, MapReduce can take advantage of data's locality, processing it close to where it's stored to reduce communication costs. Typically, a MapReduce framework (or system) consists of three operations: Map: Each worker node applies the map function to local data and saves the result to a temporary storage. Only one copy of the redundant input data is processed by a master node. Shuffle: worker nodes redistribute data based on output keys (produced by the map function), ensuring that all data associated with a single key is stored on the same worker node. Reduce: each group of output data is now processed in parallel by worker nodes, per key. This article will walk you through the Map-Reduce model's functionality step by step. Map Reduce in MongoDB The map-reduce operation has been deprecated since MongoDB 5.0. An aggregation pipeline outperforms a map-reduce operation in terms of performance and usability. Aggregation pipeline operators like $group, $merge, and others can be used to rewrite map-reduce operations. Starting with version 4.4, MongoDB provides the $accumulator and $function aggregation operators for map-reduce operations that require custom functionality. In JavaScript, use these operators to create custom aggregation expressions. The map and reduce functions are the two main functions here. As a result, the data is independently mapped and reduced in different spaces before being combined in the function and saved to the specified new collection. This mapReduce() function was designed to work with large data sets only. You can perform aggregation operations like max and avg on data using Map Reduce, which is similar to groupBy in SQL. It works independently and in parallel on data. Implementing Map Reduce with Mongosh (MongoDB Shell)  The db.collection.mapReduce() method in mongosh is a wrapper for the mapReduce command. The examples that follow make use of the db.collection.mapReduce(). Example: Create a collection ‘orders’ with these documents: db.orders.insertMany([     { _id: 1, cust_id: "Ishan Jain", ord_date: new Date("2021-11-01"), price: 25, items: [ { sku: "oranges", qty: 5, price: 2.5 }, { sku: "apples", qty: 5, price: 2.5 } ], status: "A" },     { _id: 2, cust_id: "Ishan Jain", ord_date: new Date("2021-11-08"), price: 70, items: [ { sku: "oranges", qty: 8, price: 2.5 }, { sku: "chocolates", qty: 5, price: 10 } ], status: "A" },     { _id: 3, cust_id: "Bhavesh Galav", ord_date: new Date("2021-11-08"), price: 50, items: [ { sku: "oranges", qty: 10, price: 2.5 }, { sku: "pears", qty: 10, price: 2.5 } ], status: "A" },     { _id: 4, cust_id: "Bhavesh Galav", ord_date: new Date("2021-11-18"), price: 25, items: [ { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" },     { _id: 5, cust_id: "Bhavesh Galav", ord_date: new Date("2021-11-19"), price: 50, items: [ { sku: "chocolates", qty: 5, price: 10 } ], status: "A"},     { _id: 6, cust_id: "Madan Parmar", ord_date: new Date("2021-11-19"), price: 35, items: [ { sku: "carrots", qty: 10, price: 1.0 }, { sku: "apples", qty: 10, price: 2.5 } ], status: "A" },     { _id: 7, cust_id: "Madan Parmar", ord_date: new Date("2021-11-20"), price: 25, items: [ { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" },     { _id: 8, cust_id: "Abhresh", ord_date: new Date("2021-11-20"), price: 75, items: [ { sku: "chocolates", qty: 5, price: 10 }, { sku: "apples", qty: 10, price: 2.5 } ], status: "A" },     { _id: 9, cust_id: "Abhresh", ord_date: new Date("2021-11-20"), price: 55, items: [ { sku: "carrots", qty: 5, price: 1.0 }, { sku: "apples", qty: 10, price: 2.5 }, { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" },     { _id: 10, cust_id: "Abhresh", ord_date: new Date("2021-11-23"), price: 25, items: [ { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" }  ]) Apply a map-reduce operation to the orders collection to group them by cust_id, then add the prices for each cust_id: To process each input document, define the map function: this refers the document that the map-reduce operation is processing in the function. For each document, the function maps the price to the cust_id and outputs the cust_id and price. var mapFunction1 = function() {emit(this.cust_id, this.price);}; With the two arguments keyCustId and valuesPrices, define the corresponding reduce function: The elements of the valuesPrices array are the price values emitted by the map function, grouped by keyCustId. The valuesPrice array is reduced to the sum of its elements by this function. var reduceFunction1 = function(keyCustId, valuesPrices) {return Array.sum(valuesPrices);};Apply the mapFunction1 map function and the reduceFunction1 reduce function to all documents in the orders collection: db.orders.mapReduce(mapFunction1,reduceFunction1,{ out: "map_reduce_example" }) The results of this operation are saved in the map_reduce_example collection. If the map_reduce_example collection already exists, the operation will overwrite its contents with the map-reduce operation's results. Check the map_reduce_example collection to verify: db.map_reduce_example.find().sort( { _id: 1 } ) Aggregation Alternative:You can rewrite the map-reduce operation without defining custom functions by using the available aggregation pipeline operators: db.orders.aggregate([{$group: { _id:"$cust_id",value:{$sum: "$price" } } },{ $out: "agg_alternative_1" }]) Check the agg_alternative_1 collection to verify: db.agg_alternative_1.find().sort( { _id: 1 } )Implementing Map Reduce with Java Consider the collection car and insert the following documents in it. db.car.insert( [ {car_id:"c1",name:"Audi",color:"Black",cno:"H110",mfdcountry:"Germany",speed:72,price:11.25}, {car_id:"c2",name:"Polo",color:"White",cno:"H111",mfdcountry:"Japan",speed:65,price:8.5}, {car_id:"c3",name:"Alto",color:"Silver",cno:"H112",mfdcountry:"India",speed:53,price:4.5}, {car_id:"c4",name:"Santro",color:"Grey",cno:"H113",mfdcountry:"Sweden",speed:89,price:3.5} , {car_id:"c5",name:"Zen",color:"Blue",cno:"H114",mfdcountry:"Denmark",speed:94,price:6.5} ] ) You will get an output like this:  Let's now write the map reduce function on a collection of cars, grouping them by speed and classifying them as overspeed cars.  var speedmap = function (){  var criteria;  if ( this.speed > 70 ) {criteria = 'overspeed';emit(criteria,this.speed);}}; Based on the speed, this function classifies the vehicle as an overspeed vehicle. The term "this" refers to the current document that requires map reduction. var avgspeed_reducemap = function(key, speed) {       var total =0;       for (var i = 0; i 
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Implementing MongoDb Map Reduce using Aggregation

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