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A Quick Guide to Working With Objects in JavaScript.

In this blog we will learn about JavaScript (JS) Objects. As you know, JS is one of the most popular languages for web developers.  In JS , we can directly create the objects and we don’t write class to create the object of that classes. Similar to other programming languages JS is also Object oriented programming language, which complies or satisfy the below four principles object-oriented programming  Polymorphism Encapsulation  Inheritance  Aggregation An object is a collection of properties which can be defined as key/value pairs; where each property has been assigned with the key and the value, wherein the key in the property can be the string and value can be any value. Let’s learn more about JS objects. JavaScript Objects Overview:-  Objects in JavaScript may be defined as an unordered collection of related data, of primitive or reference types, in the form of key/value pairs. These keys can be variables or functions and are called properties and methods, (respectively) in the context of an object.  All the objects in JS are derived from the parent Object constructors, and each object has many built-in methods.   Creating a JS Object:-  We can create objects in 2 ways Object literals and Properties Object Constructor. By directly creating an object instance. Object literals and properties:-  Syntax for this is object={property1:value1,property2:value2.....propertyN:valueN} let test = {..};  let emp = {  name: “Knowledge Hut”;                             message: ”Hello World”;  };   The properties name and message is known as key and assigned with the value, whereas emp is the object. property name value =”Knowledge Hut”  property message value= ”Hello World”;  Object Constructor:- In order to create an object using constructor, we need to create the function with arguments. Each argument value will be assigned to the current object, using the keyword this. <script>    function student(studId, studName,studMarks){    this.studId=studId;    this.studName=studName;    this.studMarks=studMarks;    }      s=new student(1,"APJ Abdul Kalam",450); document.write(s.studId+" "+s.studName+" "+s.studMarks);    </script>  Outputà1 APJ Abdul Kalam 450 By directly creating object instance:- We can create the object instance using the new keyword syntax for the same var objName = new Object(); <script>        var student=new Object();      student.studId=1;        student.studName="APJ Abdul Kalam";       student.studMarks=450;        document.write(student.studId+" "+ student.studName+" "+ student.studMarks);    </script>  Outputà1 APJ Abdul Kalam 450 JavaScript Objects and Properties:- Once we create an object, we can start adding the properties to the newly created objects. let test = {    firstName: "Knowledge",     lastName: "Hut" };   In the above example firstname and lastname are the properties for the object test and “Knowledge” and “Hut” are the values. Property name can be numbers and strings, when we are using numbers are property name we will be accessing them using the [] called as bracket notations. let test = {       name: "APJ Abdul Kalam",       Country : "India",       birth year: '1987',       09 : 450,       printResult : function(){           console.log("The result of 09 is ${test["09"]}`);  // here this is called bracket notation      }   }   test.printResult();   Output --> The result of 09 is 450  Property name with strings must be enclosed in quotes  let test = {      "emp name" : "APJ Abdul Kalam",  } Inherited Properties:-  Properties that are inherited from the existing object. To inherit the property we can use the method hasOwnProperty(); const test1 = new Object();   test1.prop1 = 111;    console.log(test1.hasOwnProperty('prop1')); // true Attributes of Property:-       JS has 4 attributesValue:- Property value writable:- if true the value can be changed enumerable:- if true property can be iterated over an enumeration.  configurable:- if false deletes/changes the property Accessing JavaScript Objects:-  All the JS object properties and members can be accessed using the dot notation (:). Syntax - (objectName.propertyName) EX:emp.empFirstName let emp ={       empFirstName: ‘APJ Abdul’,       empLastName:’Kalam’  };  console.log(emp.empFirstName);  console.log(emp.empLastName);    Array Notation:- Accessing object’s property via array like notation.                Syntax—objectName[‘propertyName’];  let emp ={       empFirstName: ‘APJ Abdul’,       empLastName:’Kalam’  };  console.log(emp[empFirstName]);  console.log(emp[empLastName]);  If a property contains a name space we need to place the same in quotes. let emp ={       ‘emp salary’: 25,000,       empFirstName: ‘APJ Abdul’,       empLastName:’Kalam’  }; While accessing the property which has namespace we must always use array like notation, the dot notation will give error. emp[‘emp salary’]; Changing the property Value:- Using assignment operator we can change the value of the property. let emp ={       empFirstName: ‘Abdul’,       empLastName:’Kalam’  };  emp.empFirstName = ‘APJ’;  console.log(emp); àOutput à{empFirstName: ‘APJ’, empLastName:’Kalam’} Adding new property to the object:- Once the object has been created we can add a property to the object. emp.id = 1243; Deleting a property:- Using delete operator we can delete a property from the object. Syntax—delete objectName.propertyName;  Ex-delete emp.id; To check if property exists:- Using in operator we can check if any particular property exists in the object or not. Syntax- propertyName in objectName  let student ={       studentFirstName: ‘APJ Abdul’,       studentLastName:’Kalam’,       studentPanNo:101234,       };  console.log(studentId in student);  console.log(studentPanNo in student);    Output false true Iterate using for..in loop:- Syntax – for(let key in object){ ///….  };   The this keyword:- Using this we can access the data stored in the objects. Syntax- this.propertyName  let student ={       studentFirstName: ‘APJ Abdul’,       studentLastName:’Kalam’,       studentPanNo:101234,      msg:function(){  console.log(‘Welcome to school’);  },  getStdName: function(){  return this. studentFirstName+ ‘ ’+this. studentLastName;  }       };  console.log(student. getStdName());    output APJ Abdul Kalam JavaScript Object Methods:-  All the objects have actions as long as actions are used inside the functions.Methods are defined in the same way that normal functions are defined, except that they have to be assigned as the property of an object. var objectName = {   method1: function(params) {    // ...do something   }   method2: function(params) {    // ...do something   }  };  OR  var objectName = {   method1(params) {    // ...do something   }   method2(params) {    // ...do something   }  };  OR  var objectName.method1 = {   // ...do something  }  let student ={       studentFirstName: ‘APJ Abdul’,       studentLastName:’Kalam’,       studentPanNo:101234,     };  Student.message =function(){  console.log(‘Welcome to School’);  }  Student.message();  Output Welcome to school Build in JS Object methods:-  Here are some JS built-in objects and their usage: Object.assign() --  Used to copy own properties from source to destination object. Object.create() – Used to create the new object and link to an existing object. Object.keys() – Used to create an array of keys of an object, we can also iterate through      the keys of the object. Object.values() – Used to create an array of values of an object, we can also iterate through the values of the object. Object.entities() – Used to return the array of keys/values of an object. Object.freeze() – Used to prevent removal of the existing properties of the object. Defining getters and setters:-  The getters and setters of the object are known as accessor properties. With the help of getters and setters, security is improved and malicious tampering of code is prevented. Syntax—  let obj = {    get propName() {      // getter, the code executed on getting obj.propName    },    set propName(value) {      // setter, the code executed on setting obj.propName = value    }  };    Get:  let student ={       studentFirstName: ‘APJ Abdul’,       studentLastName:’Kalam’,   get studFullName() {      return `${this.studentFirstName} ${this.studentLastName}`;    }        };  console.log(student.studFullName);    Set:-  let student ={       studentFirstName: ‘APJ Abdul’,       studentLastName:’Kalam’,   get studFullName() {      return `${this.studentFirstName} ${this.studentLastName}`;    },  set studFullName(value){  [this. studentFirstName, this. studentLastName] = value.split(" ");  }        };  student.studFullName = “APJ Abdul Kalam”;  console.log(student.studFullName); Conclusion:In this blog we explored JS objects. JavaScript is designed on a simple object-based paradigm. An object is a collection of properties, and a property is an association between a key and a value. A property's value can be a function, in which case the property is known as a method. Objects can be accessed either by dot(.) notation or array-like notation([]).   JS Objects are mutable, which means that their state can be modified after they have been created. An object provides us the ability to read our code more effectively and clearly.  

A Quick Guide to Working With Objects in JavaScript.

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A Quick Guide to Working With Objects in JavaScript.

In this blog we will learn about JavaScript (JS) Objects. As you know, JS is one of the most popular languages for web developers 

In JS , we can directly create the objects and we don’t write class to create the object of that classes. Similar to other programming languages JS is also Object oriented programming language, which complies or satisfy the below four principles object-oriented programming  

  • Polymorphism 
  • Encapsulation 
  •  Inheritance 
  •  Aggregation 

An object is a collection of properties which can be defined as key/value pairs; where each property has been assigned with the key and the value, wherein the key in the property can be the string and value can be any value. Let’s learn more about JS objects. 

JavaScript Objects Overview:-  

Objects in JavaScript may be defined as an unordered collection of related data, of primitive or reference types, in the form of key/value pairs. These keys can be variables or functions and are called properties and methods, (respectively) in the context of an object.  

All the objects in JS are derived from the parent Object constructors, and each object has many built-in methods.   

Creating a JS Object:-  We can create objects in 2 ways 

  • Object literals and Properties 
  • Object Constructor. 
  • By directly creating an object instance. 

Object literals and properties:-  Syntax for this is object={property1:value1,property2:value2.....propertyN:valueN} 

let test = {..}; 
let emp = { 
name: “Knowledge Hut”; 
                           message: ”Hello World”; 
};   

The properties name and message is known as key and assigned with the value, whereas emp is the object. 

property name value =”Knowledge Hut” 
property message value= ”Hello World”;  

Object Constructor:- In order to create an object using constructor, we need to create the function with arguments. Each argument value will be assigned to the current object, using the keyword this. 

<script>   
function student(studId, studName,studMarks){   
this.studId=studId;   
this.studName=studName;   
this.studMarks=studMarks;   
}   
  s=new student(1,"APJ Abdul Kalam",450);
document.write(s.studId+" "+s.studName+" "+s.studMarks);   
</script> 
Outputà1 APJ Abdul Kalam 450 

By directly creating object instance:- We can create the object instance using the new keyword syntax for the same var objName = new Object(); 

<script>   
    var student=new Object(); 
    student.studId=1;   
    student.studName="APJ Abdul Kalam";   
   student.studMarks=450;    
   document.write(student.studId+" "+ student.studName+" "+ student.studMarks);   
</script> 
Outputà1 APJ Abdul Kalam 450 

JavaScript Objects and Properties:- Once we create an object, we can start adding the properties to the newly created objects. 

let test = { 
  firstName: "Knowledge", 
   lastName: "Hut" }; 

 In the above example firstname and lastname are the properties for the object test and “Knowledge” and “Hut” are the values. 

Property name can be numbers and strings, when we are using numbers are property name we will be accessing them using the [] called as bracket notations. 

let test = {  
    name: "APJ Abdul Kalam",  
    Country : "India",  
    birth year: '1987',  
    09 : 450,  
    printResult : function(){  
        console.log("The result of 09 is ${test["09"]}`);  // here this is called bracket notation 
    }  
 
test.printResult();  
Output --> The result of 09 is 450 
Property name with strings must be enclosed in quotes 
let test = { 
    "emp name" : "APJ Abdul Kalam", 
} 

Inherited Properties:-  Properties that are inherited from the existing object. To inherit the property we can use the method hasOwnProperty(); 

const test1 = new Object();  
test1.prop1 = 111;  
 console.log(test1.hasOwnProperty('prop1')); // true 

Attributes of Property:-  

     JS has 4 attributes

  • Value:- Property value 
  • writable:- if true the value can be changed 
  • enumerable:- if true property can be iterated over an enumeration 
  • configurable:- if false deletes/changes the property 

Accessing JavaScript Objects:- All the JS object properties and members can be accessed using the dot notation (:). Syntax - (objectName.propertyName) 

EX:emp.empFirstName 

let emp ={ 
     empFirstName: ‘APJ Abdul’, 
     empLastName:’Kalam’ 
}; 
console.log(emp.empFirstName); 
console.log(emp.empLastName); 
 
Array Notation:- Accessing object’s property via array like notation. 
              Syntax—objectName[‘propertyName’]; 
let emp ={ 
     empFirstName: ‘APJ Abdul’, 
     empLastName:’Kalam’ 
}; 
console.log(emp[empFirstName]); 
console.log(emp[empLastName]); 

 If a property contains a name space we need to place the same in quotes. 

let emp ={ 
     ‘emp salary’: 25,000, 
     empFirstName: ‘APJ Abdul’, 
     empLastName:’Kalam’ 
}; 

While accessing the property which has namespace we must always use array like notation, the dot notation will give error. 

emp[‘emp salary’]; 

Changing the property Value:- Using assignment operator we can change the value of the property. 

let emp ={ 
     empFirstNameAbdul’, 
     empLastName:’Kalam’ 
}; 
emp.empFirstName = ‘APJ; 
console.log(emp); àOutput à{empFirstName: ‘APJ’, empLastName:’Kalam’} 

Adding new property to the object:- Once the object has been created we can add a property to the object. 

emp.id = 1243; 

Deleting a property:- Using delete operator we can delete a property from the object. 

Syntax—delete objectName.propertyName; 
Ex-delete emp.id; 

To check if property exists:- Using in operator we can check if any particular property exists in the object or not. 

Syntax- propertyName in objectName 
let student ={ 
     studentFirstName: ‘APJ Abdul’, 
     studentLastName:’Kalam’, 
     studentPanNo:101234, 
    
}; 
console.log(studentId in student); 
console.log(studentPanNo in student); 
 
Output false true 

Iterate using for..in loop:- 

Syntax – for(let key in object){ ///…. 
};   

The this keyword:- Using this we can access the data stored in the objects. 

Syntax- this.propertyName 
let student ={ 
     studentFirstName: ‘APJ Abdul’, 
     studentLastName:’Kalam’, 
     studentPanNo:101234, 
    msg:function(){ 
console.log(‘Welcome to school’); 
}, 
getStdNamefunction(){ 
return this. studentFirstName‘ ’+this. studentLastName; 
} 
    
}; 
console.log(student. getStdName()); 
 
output APJ Abdul Kalam 

JavaScript Object Methods:-  All the objects have actions as long as actions are used inside the functions.Methods are defined in the same way that normal functions are defined, except that they have to be assigned as the property of an object. 

var objectName = { 
 method1: function(params) { 
  // ...do something 
 } 
 method2: function(params) { 
  // ...do something 
 } 
}; 
OR 
var objectName = { 
 method1(params) { 
  // ...do something 
 } 
 method2(params) { 
  // ...do something 
 } 
}; 
OR 
var objectName.method1 = { 
 // ...do something 
} 
let student ={ 
     studentFirstName: ‘APJ Abdul’, 
     studentLastName:’Kalam’, 
     studentPanNo:101234, 
   }; 
Student.message =function(){ 
console.log(‘Welcome to School’); 
} 
Student.message(); 
Output Welcome to school 

Build in JS Object methods:-  Here are some JS built-in objects and their usage: 

  1. Object.assign() --  Used to copy own properties from source to destination object. 
  2. Object.create() – Used to create the new object and link to an existing object.
  3.  Object.keys() – Used to create an array of keys of an object, we can also iterate through      the keys of the object. 
  4. Object.values() – Used to create an array of values of an object, we can also iterate through the values of the object. 
  5. Object.entities() – Used to return the array of keys/values of an object. Object.freeze() – Used to prevent removal of the existing properties of the object. 

Defining getters and setters:- The getters and setters of the object are known as accessor properties. With the help of getters and setters, security is improved and malicious tampering of code is prevented. 

Syntax— 
let obj = { 
  get propName() { 
    // getter, the code executed on getting obj.propName 
  }, 
  set propName(value) { 
    // setter, the code executed on setting obj.propName = value 
  } 
}; 
 
Get: 
let student ={ 
     studentFirstName: ‘APJ Abdul’, 
     studentLastName:’Kalam’, 
 get studFullName() { 
    return `${this.studentFirstName} ${this.studentLastName}`; 
  } 
      }; 
console.log(student.studFullName); 
 
Set:- 
let student ={ 
     studentFirstName: ‘APJ Abdul’, 
     studentLastName:’Kalam’, 
 get studFullName() { 
    return `${this.studentFirstName} ${this.studentLastName}`; 
  }, 
set studFullName(value){ 
[this. studentFirstName, this. studentLastName] = value.split(" "); 
} 
      }; 
student.studFullName = “APJ Abdul Kalam”; 
console.log(student.studFullName); 

Conclusion:

In this blog we explored JS objectsJavaScript is designed on a simple object-based paradigm. An object is a collection of properties, and a property is an association between a key and a value. A property's value can be a function, in which case the property is known as a method. Objects can be accessed either by dot(.) notation or array-like notation([])  JS Objects are mutable, which means that their state can be modified after they have been created. An object provides us the ability to read our code more effectively and clearly.  

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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The transporter variable is storing the mail object.  let transporter = nodemailer.createTransport({       host: "smtp-relay.sendinblue.com",       port: 587,       auth: {         user: process.env.USER,         pass: process.env.PASS,       },     });Open SMTP tab in your sendinmail account and cross check the host and port.In the auth object, we are passing the user and password from the environment variable.Send the mail using sendMail method.// send mail with defined transport object     let info = await transporter.sendMail({       from: from, // sender address       to: to, // list of receivers       subject: subject, // Subject line       text: text, // plain text body     });It returns a Promise of Send Message Info. In the end, it is returning the message id.  Express Route The sendEmail method is ready.  Let’s create an express route for it. This is the API endpoint using which we can access the sendEmail function. Open the mail-api.js in the code editor and paste the below code. constexpress = require("express");  constrouter = express.Router();  constsendMailMethod = require("../src/send-mail");  // Post request to send an email  router.post("/sendmail", async (req, res) => {  try {  constresult = awaitsendMailMethod(req.body);  // send the response  res.json({  status:true,  payload:result          });      } catch (error) {  console.error(error.message);  res.json({  status:false,  payload:"Something went wrong in Sendmail Route."          })      }  }) module.exports = router; The express framework provides a Router method to create different HTTP methods. Here, we have created a POST method to send the mail.  Instead of extracting the req.body parameters, we passed it as it is. The benefit of this approach is that if there is a change in argument or position, then we would not have to change it in all the places.  In the end, we are exporting the router. Now, this can be used in the server side. Express Server Now, it’s time to create a server and expose the routes on it. Open the index.js and paste the below code in it. "use strict";  constexpress = require("express");  constbodyParser = require("body-parser");  constcors = require("cors");  constapp = express();  constmailAPI = require("./routes/mail-api.js");  // Express body parser  app.use(cors());  app.use(bodyParser.json());  app.use(  bodyParser.urlencoded({  limit:"50mb",  extended:false,  parameterLimit:50000    })  );  // use the routes specified in route folder  app.use("/api/v1", mailAPI);  constport = process.env.PORT || 4444;  //listen to the server  app.listen(port, function () {  console.log(`listening to the port ${port} .....`);  }); The route is available on /api/v1/sendmail. Run the server. $ node index.js  listening to the port 4444 ..... Send an Email using API There are couple of methods to test the API. Using the Postmanor using the Curl command. Using Postman Install Postman on your machine if it is not installed. Create a POST request. URL: http://localhost:4444/api/v1/sendmail Content Type: JSON – Body tab > select JSON from dropdown Request Body:  {  "from": "hello@schadokar.dev",  "to": ["shubham@schadokar.dev"],  "subject": "Mail from Nodemailer",  "text": "Sending an email using nodemailer package."  } Hit Send. Make sure the server is running. On Success, the response returns the message id. Now, check your mailbox. If you are unable to find the mail in your Inbox, check the promotional mail folder. Using Curl CommandOpen the terminal or cmd.In the below curl command, change the parameters and enter.curl -X POST http://localhost:4444/api/v1/sendmail -H "Content-Type:application/json" -d '{"from": "hello@schadokar.dev","to": ["shubham@schadokar.dev"],"subject": "Mail from Nodemailer", "text": "Sending an email using nodemailer package."}'In this example, we have sent a simple text message to the recipient.  Nodemailer also gives you an option to send the message in HTML format. Mail template Open the mail.html in the code editor and paste the below code. 
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Learn Nodemailer Module in Node.js

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Full Stack Development – the Hottest Developer Skill for the Digital Age

With over 1.7 billion websites worldwide and 4.54 billion people using the internet actively, the need for heightened customer experience is on the rise. This is one of the major reasons why professionals who are adept at handling both the client-side and server-side interfaces of an application/website have become more important than ever. It has been estimated that by the next decade, there will be 300,000 new developer jobs in US. The Full Stack developer role is the No.1 position to be filled in 2020 according to 38% of hiring managers. This is closely followed by the role of a back-end developer.Handsome pay packagesThe average annual salary for a full-stack developer is about $110,737 per annum. Even beginners are offered about $58,000 per year and on the other hand, experienced professionals would earn up to $188,253 per year.These professionals are paid handsomely because enterprises are aware that a full stack developer does the job of two professionals (back-end and front-end developer).Plenty of growth opportunitiesAs per reports by The United States Bureau of Labor Statistics, full-stack development job opportunities will increase from 135,000 to 853,000 by the year 2024. This is quite promising for aspiring full stack developers as an ocean of opportunities will be available for them in both startups as well as in multi-national organizations.Skills to become a Full Stack developerBecoming a full-fledged full stack developer is not child’s play. It takes a wide range of skills to become a good full stack developer. Below are the mandatory skills:Front-end skills: They should be well-versed with basic front-end technologies like HTML5, CSS3, and JavaScript. They should also be comfortable working with front-end frameworks or third-party libraries such as JQuery, SASS, and AngularJS.Programming languages: They should be aces in at least one server-side coding language like Java, Python, Ruby or .Net.Databases: They should be efficient at handling data from databases like MySQL, MongoDB, Redis, Oracle and SQLServer.Version control systems (VCS): Full stack developers must be aware of Git so that they can make appropriate changes to the codebase.Basic design skills: Awareness about the basic prototype design and UI/UX design is essential to become a successful full stack developer.Server and API: They should have adequate exposure to Apache or Linux servers as well as web services.The way forward for Full Stack developersThe growing demand for full-stack developers is due to the ample benefits they offer to organizations. With technology evolving at a rapid pace, foresighted companies will keep adding them to their workforces. Full stack development became the No.1 developer skill because these developers are trained to multi-task various technologies and products. For aspiring full stack developers out there, now is the best time to make the most of these opportunities.Real products require real challenges. Check out our live online workshops and build your portfolio of projects.
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Full Stack Development – the Hottest Develop...

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What are React Component Lifecycle Methods

React is the most popular JavaScript library used to create interactive UI for web applications. It is a component-based library where different parts of a webpage can be encapsulated by components which are quite easy to create, manage and update. React allows us to create Single Page Applications which maintain the state of individual components on an app without having to reload it.  What are React Components? Developers who are new to JavaScript libraries and frameworks like React and Angular might ask the question, “What is a component?” Well, in very simple words, a component is a unit of code which includes JavaScript and HTML to build a part of a web page. It acts like a custom HTML element. It is reusable and can be as complex as you want it to be. For example, imagine that you are creating a very basic application with header, footer, and body. The header can be a component; the footer can be another component and the body can be yet another one or even might consist of multiple components.One of the most useful characteristics of React is its ability to integrate reusable components in a project. Reusability is the characteristic of a component which allows it to be used again, thereby reducing the amount of code a developer has to write. In our example here, the header can be a reusable component and can be used on all the pages of the application, which makes it easy to maintain and update. What does a component look like? Here is a simple example of a react component which contains a simple form. This is a class-based component. React also supports function-based components. As you can see in the code below, App is a user-defined class which inherit from React’s Component class and it has a render method which returns HTML code. As the name suggests, the render method returns and renders HTML to our browser. Every component has to return HTML which is rendered to the user’s browser by render method.import React, { Component } from 'react';  class App extends Component {    handleChange(event) {      this.setState({value: event.target.value});    }    render() {      return (                              Username:                                            Password:                                              );    }  }    export default App; In the above example, we have created a login form where there are 2 input boxes for the user to enter their username and password and then submit the form. We have assigned an event handler to form which will handle the login event in component.We have exported our component (using export default App) so that it can be rendered inside other components.This is a very basic example of component, but this can be as complex as you want it to be. But it is always advised to make your component independent and it should represent only a part of your page which can be reusable as well. It can return complex HTML included with JavaScript to handle complex features in your application.Component as a class React allows us to create component in the form of class as well as functions. While creating component as class you need to define a class which extends React.Component class. Component class has many features which the deriving class can use to maintain the state throughout the lifecycle. In case you want to have more custom features, you can create your own base component class which derives from Component class, and then your component classes can derive from your base component class. What do we mean by Component Lifecycle?Lifecycle of a component is the set of different stages (also known as lifecycle hooks) a component goes through while it is active. Stages could be when a component is created or when any changes are made to the component and many others. There are different methods executed by React at different points of time between when a component is created and at the end when it is destroyed and not in use. One such hook or method we have already seen in the code above, which is render(), and it is executed by React to render the component. We can override these methods and perform certain tasks in those methods, but every lifecycle serves a different purpose and it can be a nightmare if we ask them to do something that they aren’t supposed to or are not very good at. As a developer we should be aware of what those different stages are, what happens in those stages, in what order they execute and how we can make the best use of it. Understanding the lifecycle of components also helps us predict behavior of a component at different stages, which makes it easier to work with them. Managing a large set of components in an application can get you in trouble if you do not know how they work behind the scenes.Props and State Before we start with lifecycle hooks, lets understand what props and state are as they are most commonly used properties in component classes. Props It is a keyword which means properties. Props are used by callers of components to pass properties to the called component in a uni-directional flow. For example, if Parent component renders child component, it can define props and pass them to the child component which is then available and accessible by this.props. Another thing to note here is that props is a ready-only attribute which means data which is passed by parent should not be changed by client components. State State is a plan JavaScript object which defines the current state of any component. It is user defined and can be changed by lifecycle hooks. Ideally state should contain only data which is going to be rendered on DOM. State has getter and setter methods this.getState() and this.setState() which as the names suggest are used to access and update State. It is good practice to use setState method to update State and treat State as an immutable JavaScript object.Since there are many lifecycle hooks a component goes through, it would easier to understand if we start with the hooks which are executed when a component is created.Lifecycle hooks while Mounting [These lifecycle hooks are executed in order as listed, when a component is created]constructor(props) This is not a component lifecycle hook, but it is important to mention here and to be aware that Constructor is executed before it is mounted. Constructor receives props(properties of a component) as an argument which then can be passed to base class using super keyword if we define the constructor.  It is not mandatory to define constructor in component class, but if you do to perform any logic, then you need to call base constructor using super keyword.  Mainly constructors are used: To Setup local state of component with this.state To bind event handler methods. This is what a simple constructor would look like.import React, { Component } from 'react';  class App extends Component {    constructor(props) {      super(props);      this.state = { value: 0 };      this.handleClick = this.handleClick.bind(this);    }  } this.state should be called only inside constructor, to update the state in other methods use this.setState() method.  If constructor is required to do any heavy tasks, it will impact the performance of component, and you should be aware of this fact.  getDerivedStateFromProps(props, state) After constructor, this lifecycle hook is called before render method is executed. It is called while mounting as well as whenever props have changed. This is not very commonly used, only in cases where props can change, and you need to update state of the component. This is the only use case where you should implement this lifecycle hook.This method is executed on every render and cannot access component instance.import React, { Component } from 'react';  class App extends Component {    getDerivedStateFromProps(props, state) {      if (props.value !== state.prevValue) {        return {          prevValue: props.value        };      }      return null;    }    }render() This is the method which is required to be implemented in component class. It can access props and state. This is where you can write your html and jsx code. You can also render child components in this method which will then be rendered as well. Before completing the lifecycle of parent, lifecycle of all child components will be finished. All this html and jsx is then converted to pure html and outputs in DOM. JSX is a JavaScript extension which creates React elements. It looks more like template language but it is empowered by JavaScript which allows it to do a lot more. It can embed expressions . JSX has different set of attributes than what we have in html. For example, while creating html using JSX you need to use attribute “className” instead of class. This is what a typical render method looks like:import React, { Component } from 'react';   class App extends Component {   render() {         return (        Click to go Home { this.state.home }       Go to Home         );   } } Alternatively you can also use React.createElement() method to create html using JSX.const element = React.createElement(       'h1',       {className: 'hello'},       'Hello, world!'     );componentDidMount() As the name suggests, componentDidMount() is invoked after the component is mounted, which means html has been added to DOM tree. It is a very commonly used lifecycle hook, as it allows you to do a lot of things including causing side-effects, setting up any subscriptions, or loading data from external endpoints. If you setup any subscription using this method, make sure to unsubscribe them in componentWillUnmount() lifecycle hook. You shouldn’t update state in this method using this.State() as it may cause performance issues. For assigning initial state you should use constructor(). import React, { Component } from 'react';  class App extends Component {    componentDidMount(){    // Component is rendered and now external calls can be made.      this.getDataAfterTimeOut();    }    getDataAfterTimeOut(){      setTimeout(() => {        this.setState({          data: 'Data is fetched'        })      }, 1000)    }  } Lifecycle hooks while Updating [Next set of lifecycle hooks are executed while a component is updating which can be caused by changes to props(properties) or state of component. These are invoked in order as listed below.] getDerivedStateFromProps(props, state) We have already talked about this. This is invoked every time a component is changed or updated. Any changes in properties or state which causes the component to be changed will invoke this method. shouldComponentUpdate(nextProps, nextState) shouldComponentUpdate() is invoked before rendering (not on initial rendering) but only when props or state has been changed. Even though it is not recommended you can use this lifecycle hook to control the re-rendering. This can lead to performance issues as well as bugs, so be careful while doing that.  In this method nextProps can be compared with this.props and nextState can be compared with this.state. This method can return true or false depending on whether you want to continue rendering by skipping the next lifecycle hooks. In either case it can’t prevent re-rendering of child components. Note that this method defaults to true which will not skip rendering and next lifecycle hooks and continue with execution. import React, { Component } from 'react';  class App extends Component {    shouldComponentUpdate(nextProps, nextState) {  // This value will determine if lifecycle execution is to be skipped or continued.      return nextProps.value != this.props.value;    }  } render() After shouldComponentUpdate lifecycle hook render is called, which we have already talked about, it prepares html and jsx code which then outputs to DOM. getSnapshotBeforeUpdate() getSnapshotBeforeUpdate() is invoked right before the recent changes are added to DOM. This lifecycle hook gives us an opportunity to capture any details we need from the DOM before it is updated with new content. For example, if you want to know the scrolling position of the user, which should be restored after the DOM has changed. Use cases for this lifecycle, while rare, can be of great value at times. The snapshot value which is captured and returned by this hook is passed as a parameter to another lifecycle hook componentDidUpdate() which we will talk about next. import React, { Component } from 'react';  class App extends Component {    getSnapshotBeforeUpdate (prevProps, prevState) {  // implementing this method here allows us to capture the snapshot of current dom tree.      if (this.state.value != prevState.value) {        return table.scrollHeight - table.scrollTop      }      return null    }  }componentDIdUpdate(prevProps, prevState, snapshot) componentDidUpdate is invoked when DOM is updated. It is only called on update, not on initial rendering. You can use this method to make data requests after checking if props have changed. You can also call setSatate() in this method, but make sure to wrap that in a condition else it will cause an infinite loop forcing re-rendering and affecting performance issues. Also it should be noted that value for snapshot will only be available if you have implemented getSnapshotBeforeUpdate() in your component; else value for snapshot will be undefined. Here is an example of componentDidUpdate. This is a very basic example where we have captured snapshot by implementing get Snapshot Before Update lifecycle hook. After that componentDidUpdate is invoked and content is overwritten with new dataimport React, { Component } from 'react';  class App extends Component {    getSnapshotBeforeUpdate(prevProps, prevState) {  // implementing this method here allows us to capture the snapshot of current dom tree.      document.getElementById("divContent").innerHTML =      "Before the update content is " + prevState.content;    }    componentDidUpdate(prevProps, prevState, snapshot) {  // You can access snapshot here to get data from dom before it was updated.      document.getElementById("divContent").innerHTML =      "New content updated " + this.state.content;    }  } import React, { Component } from 'react';  class App extends Component {    getSnapshotBeforeUpdate(prevProps, prevState) {  // implementing this method here allows us to capture the snapshot of current dom tree.      document.getElementById("divContent").innerHTML =      "Before the update content is " + prevState.content;    }    componentDidUpdate(prevProps, prevState, snapshot) {  // You can access snapshot here to get data from dom before it was updated.      document.getElementById("divContent").innerHTML =      "New content updated " + this.state.content;    }  } UnMounting [This is where lifecycle of a component ends when component is destroyed and removed from DOM. While Unmounting React gives us an opportunity to do something before component is destroyed, it can include clearing objects which have occupied memory to avoid memory leaks.] componentWillUnMount() componentWIllUnMount() is executed right after component is unmounted which means it is removed from DOM and destroyed. But before it is removed and destroyed, React gives us an opportunity to perform any cleanup we want to. For example, you might have setup subscriptions initially in componentDidMount() which you should unsubscribe when component is destroyed to avoid memory leaks in your application. You can also remove event listeners which were subscribed before. In this lifecycle hooks you should not update state of your component because component is not going to re-render now.import React, { Component } from 'react';  class App extends Component {    componentWillUnmount() {  // Component will be removed from DOM now.        // Unscubscribe subscriptions and events here.  document.removeEventListener("click", this.handleSubmit);    }  }Conclusion In this article we talked about React, its components and its different lifecycles. It is very crucial to understand the different opportunities that React provides through these lifecycle methods. There are many rules we need to follow while working with these hooks. Making them do something they can’t handle can cause performance issues or even infinite loops at times.  These lifecycle hooks work with props and state which are the most used properties of component class. Changes in state and props trigger different lifecycle hooks and even re-render the dom which is something you should be aware of. These lifecycle hooks are provided to intercept the different stages a component goes through and make the best use of it, but without understanding how they work it can break your application by causing performance issues or memory leaks. Hope this has been helpful. 
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What are React Component Lifecycle Methods

React is the most popular JavaScript library us... Read More