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Introduction to Mongo DB

MongoDB, a highly scalable No-SQL database, is used for storing information in the form of JSON strings, where the structure of the table is not fixed (unlike in SQL database). So, the advantage here is that with the help of MongoDB, we can make quick changes in our entities without actually changing the database. MongoDB is available in multiple variants and what you choose would depend on the type of development you are looking for. You can download and install the relevant server as per your operating system from here.  If you are already a Mongo user then you may have had the chance to work with the huge number of operations that Mongo provides for storing and retrieving information in a database.If you want to brush up the same before starting on this article, refer to the basics of MongoDB here. In this article, we will learn about how we can use a MongoDB database with NodeJS.  But before do that, let’s delve a little into NodeJS. Getting started with NodeJS  So what is Node JS, and why do we use it? NodeJS is a backend JavaScript runtime environment that has become a favorite with developers and designers alike, due to the marvellous advantages it offers such as minimalism, speed, and compatibility with JavaScript. Not just individual programmers but world-class top tech companies around the world are using NodeJS as their backend tech stack because of the advantages it offers.   The beauty of NodeJs lies in the fact that it allows developers to write frontend abstractions with backend written in NodeJS. We will write our first NodeJS program here but before that, we have to install NodeJs, which is pretty straightforward. Installing NodeJs Plugin for MongoDB:Follow these steps to install Node JS  Install NPM (Node Package Manager).  The Node Package Manager) plugin is used to install various NodeJS plugins with a single command. Double-check that you have npm installed in your system by simply running this command in your terminal: $ npm -v[Text Wrapping Break]6.13.6  Install the Node from NodeJs Website >> NodeJS.   See the type of Operation system and download the version as per your platform compatibility.  Follow the installation guide as suggested by the installer.  Check the node version by running this command in your terminal  $ node -v[Text Wrapping Break]v8.11.4  If you have installed Node before NPM, you will probably need to update your NPM.   npm install npm@latest -g  Installing MongoDB Node.js Driver  The Mongo NodeJS driver allows us to interact with the MongoDB databases from NodeJs applications. To install MongoDB Node.js driver, run this command in your terminal.   npm install mongodb   To see the list of current drivers installed in the system, run the following command:  npm list mongodb  If you are stuck or have issues with installation of the drivers, then this official documentation is a good reference to go through.  Now that we are ready with both the database and NodeJS backend, let’s move ahead and create a simple NodeJs project. The aim of this project is to insert and retrieve information from the database. Using Node.JS to connect to MongoDB database   To do this, we will write a simple Node.js script which will connect to our database. And then we will perform an operation to list all the databases in our cluster.Cluster? What is a cluster?A cluster is nothing but a set of nodes that carry the copies of your database. At a high level, you can say, your database is stored inside a cluster. 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Let’s Code! We will begin with Importing the Mongo Client as shown below: const {MongoClient} = require('mongodb');  To connect to the MongoDB database we have to import the MongoClient class from the MongoDB module, the instance of which can be used to connect to the cluster or for accessing the database from that cluster. Next step is to use a Main() function, where we can call other functions and can get connected to MongoDB cluster. const uri = "mongodb+srv://<put-your-username>:<put-your-password>@<write-your-cluster-url>/test?retryWrites=true&w=majority";   Note: You need to update your password and username for the user. Now that we are ready with our URI, create an instance of MongoClient as below: const client = new MongoClient(URI);  Your instance is ready, so now you can use MongoClient to connect to the cluster by calling client.connect() as below:  await client.connect();  We have used the await keyword so as to ensure that it blocks any further execution until our operation is completed. And that’s it. We are ready to interact with our database. Let’s try it out by simply printing the list of all the databases in our cluster.  await listAllDatabases(client);  You can put any name to the above function. The next step is to finally put all the functions together and wrap them in a try/catch block in order to handle any errors. try   await client.connect();   await listAllDatabases(client);catch (e) {    console.error(e);}  And, close the connection as below:  finally { await client.close(); }  No, let’s put everything together and call our main function() as:  async function main(){ const uri = "mongodb+srv://<your-username>:<your-password>@<your-cluster-url>/test?retryWrites=true&w=majority"; const client = new MongoClient(uri); try {// Connect to the MongoDB cluster await client.connect(); // Here make the DB calls or some operations await  listAllDatabases(client);  catch (e) {    console.error(e); } finally { await client.close(); }  Break]main().catch(console.error);  //To see if there are aby errorsLet’s use our function “listAllDatabases” to list all the databases in our cluster.  async function listAllDatabases(client){  databasesList = await client.db().admin().listAllDatabases(); console.log("Databases List Is:");[Text Wrapping Break]    databasesList.databases.forEach(db => console.log(` - ${db.name}`));};  If you can’t wait to see your output, then all that is left to do is to save it. Save your file as list.js.  Time to execute the NodeJs script. Let’s execute the script by running the following command in our terminal:  (Ensure that the server is running and up!) node list.js  The output should come as below:  Databases: - data_books - data_gates - data_houses - data_nodes- data_tables- admin - local  Now that we are running with the database, let’s see the different data types they are supported on.  Mongo DB data typesHave you heard of BSON? BSON is a binary-encoded format of JSON. Documents in MongoDB are stored in the format of BSON. Here is a list of typically used data types supported by MongoDB: String − It is used to store the data. It should be UTF-8 valid. Integer − This data-type is used to store a numerical value. Depending on our server, Integer can be either of 32 bit or 64 bit. Boolean − To store a boolean (true/ false) value we use this type of data type. Double − Used for storing floating-point values. Arrays − This type of data-type is used for storing list or arrays. Timestamp - This type of data-type is used to check if an element has been modified or added. Min/ Max keys − We can use min or max data types for comparing the value against the lowest and highest BSON elements and vice-versa. Object − This data type stores embedded documents. (A document that contains another document in the form of the key-value pair) Null − This type of data-type is used by MongoDB to store a Null value. Symbol − It is not supported by a shell, but if it gets a symbol from the database, it is converted into a string. So it’s quite identical to a string data type. Regular expression − These MongoDB data types stores regular expressions in MongoDB. It maps directly to JavaScript Regular Expression. Date −  This type of data-type is used to store the date or time. We can also use our date or time by simply creating an object of Date and passing elements like day, month, year into it. Object ID − Mongo uses this type of datatype to store the document’s ID. Binary data − Typically used to store binary data. Mongo DB and CollectionsA database can have multiple collections. A collection is a table that contains all your documents. We can create a collection as follows:  const collection = db.createCollection(name, options), or  const collection = db.collection(‘books’);     where, name is the connection name which can be anything, The option is a configuration document used for specifying the collection and is optional. We can list the following options while creating a collection: capped, autoIndexId, max, and size. createCollection() is an inbuilt method in MongoDB, which is used to create a new collection in database as shown above. Note: In MongoDB, a collection is never created until it gets some content!  db.collection('check', {strict:true}, function(err, collection) {});    So, this code will never create a collection until and unless you specify and insert it in the document.  ConclusionToday we learnt the basics of MongoDB, and how and why MongoDB is compatible with NodeJS. We also looked at how we can connect to our MongoDB database from NodeJS script, and found a cool demo of listing out the names of all the databases in our cluster. There are many activities that we can do with NodeJS in our database which involves the basic CRUD operations like insert, update, remove, or making a query in our collection.  And if you get stuck, see the official documentation of all of them here. It has plenty of features that make our job easier.  Happy Learning! :)

Introduction to Mongo DB

10K
Introduction to Mongo DB

MongoDB, a highly scalable No-SQL database, is used for storing information in the form of JSON strings, where the structure of the table is not fixed (unlike in SQL database). So, the advantage here is that with the help of MongoDB, we can make quick changes in our entities without actually changing the database. 

MongoDB is available in multiple variants and what you choose would depend on the type of development you are looking for. You can download and install the relevant server as per your operating system from here.  

If you are already a Mongo user then you may have had the chance to work with the huge number of operations that Mongo provides for storing and retrieving information in a database.

If you want to brush up the same before starting on this article, refer to the basics of MongoDB here. 

In this article, we will learn about how we can use a MongoDB database with NodeJS.  

But before do that, let’s delve a little into NodeJS. 

Getting started with NodeJS  

So what is Node JS, and why do we use it? 

NodeJS is a backend JavaScript runtime environment that has become a favorite with developers and designers alike, due to the marvellous advantages it offers such as minimalism, speed, and compatibility with JavaScript. Not just individual programmers but world-class top tech companies around the world are using NodeJS as their backend tech stack because of the advantages it offers.   

The beauty of NodeJs lies in the fact that it allows developers to write frontend abstractions with backend written in NodeJS. We will write our first NodeJS program here but before that, we have to install NodeJs, which is pretty straightforward. 

Installing NodeJs Plugin for MongoDB:

Follow these steps to install Node JS  

  • Install NPM (Node Package Manager).  

The Node Package Manager) plugin is used to install various NodeJS plugins with a single command. 

Double-check that you have npm installed in your system by simply running this command in your terminal: 

$ npm -v[Text Wrapping Break]6.13.6  
  • Install the Node from NodeJs Website >> NodeJS  
  • See the type of Operation system and download the version as per your platform compatibility.  
  • Follow the installation guide as suggested by the installer.  
  • Check the node version by running this command in your terminal  
$ node -v[Text Wrapping Break]v8.11.4  
  • If you have installed Node before NPM, you will probably need to update your NPM.  
npm install npm@latest -g  

Installing MongoDB Node.js Driver  

The Mongo NodeJS driver allows us to interact with the MongoDB databases from NodeJs applications. To install MongoDB Node.js driver, run this command in your terminal.   

npm install mongodb   

To see the list of current drivers installed in the system, run the following command:  

npm list mongodb  

If you are stuck or have issues with installation of the drivers, then this official documentation is a good reference to go through.  

Now that we are ready with both the database and NodeJS backend, let’s move ahead and create a simple NodeJs project. The aim of this project is to insert and retrieve information from the database. 

Using Node.JS to connect to MongoDB database   

To do this, we will write a simple Node.js script which will connect to our database. And then we will perform an operation to list all the databases in our cluster.

Introduction to Mongo DB

Cluster? What is a cluster?

A cluster is nothing but a set of nodes that carry the copies of your database. At a high level, you can say, your database is stored inside a cluster. To work on databases with Node, the easiest way is to use Atlas service which is MongoDB’s fully-managed database. If you are still unfamiliar with these terms, you can go through the complete documentation here   

Connecting MongoDB

Now that we have all our installations in place, let’s get started with connecting our database from NodeJs. Let’s Code! 

We will begin with Importing the Mongo Client as shown below: 

const {MongoClient} = require('mongodb');  

To connect to the MongoDB database we have to import the MongoClient class from the MongoDB module, the instance of which can be used to connect to the cluster or for accessing the database from that cluster. 

Next step is to use a Main() function, where we can call other functions and can get connected to MongoDB cluster. 

const uri = "mongodb+srv://<put-your-username>:<put-your-password>@<write-your-cluster-url>/test?retryWrites=true&w=majority";   

Note: You need to update your password and username for the user. 

Now that we are ready with our URI, create an instance of MongoClient as below: 

const client = new MongoClient(URI);  

Your instance is ready, so now you can use MongoClient to connect to the cluster by calling client.connect() as below:  

await client.connect();  

We have used the await keyword so as to ensure that it blocks any further execution until our operation is completed. 

And that’s it. We are ready to interact with our database. Let’s try it out by simply printing the list of all the databases in our cluster.  

await listAllDatabases(client);  

You can put any name to the above function. 

The next step is to finally put all the functions together and wrap them in a try/catch block in order to handle any errors. 

try   await client.connect();   await listAllDatabases(client);catch (e) {    console.error(e);}  

And, close the connection as below:  

finally { await client.close(); }  

No, let’s put everything together and call our main function() as:  

async function main(){ const uri = "mongodb+srv://<your-username>:<your-password>@<your-cluster-url>/test?retryWrites=true&w=majority"; const client = new MongoClient(uri); try {// Connect to the MongoDB cluster await client.connect(); // Here make the DB calls or some operations await  listAllDatabases(client);  catch (e) {    console.error(e); } finally { await client.close();  Break]main().catch(console.error);  //To see if there are aby errors

Let’s use our function “listAllDatabases” to list all the databases in our cluster.  

async function listAllDatabases(client){  databasesList = await client.db().admin().listAllDatabases(); console.log("Databases List Is:");[Text Wrapping Break]    databasesList.databases.forEach(db => console.log(` - ${db.name}`));};  

If you can’t wait to see your output, then all that is left to do is to save it. Save your file as list.js.  

Time to execute the NodeJs script. Let’s execute the script by running the following command in our terminal:  

(Ensure that the server is running and up!) 

node list.js  

The output should come as below:  

Databases: - data_books - data_gates - data_houses - data_nodes- data_tables- admin - local  

Now that we are running with the database, let’s see the different data types they are supported on.  

Mongo DB data types

Have you heard of BSON? BSON is a binary-encoded format of JSON. Documents in MongoDB are stored in the format of BSON. Here is a list of typically used data types supported by MongoDB: 

  • String − It is used to store the data. It should be UTF-8 valid. 
  • Integer − This data-type is used to store a numerical value. Depending on our server, Integer can be either of 32 bit or 64 bit. 
  • Boolean − To store a boolean (true/ false) value we use this type of data type. 
  • Double − Used for storing floating-point values. 
  • Arrays − This type of data-type is used for storing list or arrays. 
  • Timestamp - This type of data-type is used to check if an element has been modified or added. 
  • Min/ Max keys − We can use min or max data types for comparing the value against the lowest and highest BSON elements and vice-versa. 
  • Object − This data type stores embedded documents. (A document that contains another document in the form of the key-value pair) 
  • Null − This type of data-type is used by MongoDB to store a Null value. 
  • Symbol − It is not supported by a shell, but if it gets a symbol from the database, it is converted into a string. So it’s quite identical to a string data type. 
  • Regular expression − These MongoDB data types stores regular expressions in MongoDB. It maps directly to JavaScript Regular Expression. 
  • Date −  This type of data-type is used to store the date or time. We can also use our date or time by simply creating an object of Date and passing elements like day, month, year into it. 
  • Object ID − Mongo uses this type of datatype to store the document’s ID. 
  • Binary data − Typically used to store binary data. 

Mongo DB and Collections

A database can have multiple collections. A collection is a table that contains all your documents. We can create a collection as follows:  

const collection = db.createCollection(name, options), or 
const collection = db.collection(‘books’);    

where, 

  • name is the connection name which can be anything, 
  • The option is a configuration document used for specifying the collection and is optional. 
  • We can list the following options while creating a collection: capped, autoIndexId, max, and size. 
  • createCollection() is an inbuilt method in MongoDB, which is used to create a new collection in database as shown above. 

Note: In MongoDB, a collection is never created until it gets some content!  

db.collection('check', {strict:true}, function(err, collection) {});  

 So, this code will never create a collection until and unless you specify and insert it in the document.  

Conclusion

Today we learnt the basics of MongoDB, and how and why MongoDB is compatible with NodeJS. We also looked at how we can connect to our MongoDB database from NodeJS script, and found a cool demo of listing out the names of all the databases in our cluster. There are many activities that we can do with NodeJS in our database which involves the basic CRUD operations like insert, update, remove, or making a query in our collection.  

And if you get stuck, see the official documentation of all of them here. It has plenty of features that make our job 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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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...

With over 1.7 billion websites worldwide and 4.54 ... Read More

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