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Understanding Constructors With React Components

The React Constructor is a method that’s automatically called during the creation of an object from a class. Simply put, the constructor, like its name, is a great tool to build things.Constructors are used for two key objectives:To initialize the local state of the component by assigning an object to this.stateTo bind event handlers that occur in the componentIn this blog, we’ll take you through all you need to understand about React constructors including the rules to be followed while implementing them. We will also look at how to bind events all in one place and take note of how to assign values accurately.What is a Constructor?In a class, a constructor is a method that is automatically called when an object of that class is created. Typically, this is how it works:Syntax:Constructor(props){     super(props);   }A couple of points to note about a constructor are:It is not necessary to have a constructor in every component.It is necessary to call super() within the constructor. To set property or use 'this' inside the constructor it is mandatory to call super().We must remember that the setState() method cannot be used directly in the constructor(). Use 'this.state' to assign the initial state in the constructor. The constructor uses this.state to assign initial state, and other methods should use set.state().Call super(props) Before Using this.propsIn React, the constructor is called during component creation and before mounting. If you want to implement the constructor for a React component, call the super(props) method before any other statement. Otherwise, this. props will be undefined in the constructor and create bugs.constructor() {  console.log(this.props); }Using super(props) is simple. We just have to call it in the constructor method of our child component:constructor(props) {  super(props);  console.log(this.props); }Never Call setState() Inside constructor()The constructor is the ideal place to set up your component's initial state. Instead of using setState() in other methods, you will need to assign the initial state directly.class Hello extends React.Component {    constructor(props) {    super(props);    this.setState({   title: 'This is the first test'    }); }     render() {     return <div>{this.state.title} </div>   } }   ReactDOM.render(<Hello />, document.getElementById('container'));When you use the setState() method in React, it does more than just assign a new value to this. state. It also re-renders the component and all its children. Additionally, if you are trying to update a class that was defined inside of a constructor, you will receive an error, so we should avoid setState() in constructors because it is the only place we directly assign the initial state to this.state.constructor(props) {  super(props);  this.state = {    name 'kapil',    age: 22,  }; }When creating a component, you should avoid setting values directly from the component's properties. Do it as follows:constructor(props) {  super(props);  this.state = {    name: props.name,  }; }If you try to change the name property in the state object, it will not work. If you want to modify this property later, you should not use setState(). Instead, access the name property directly in your code by using this.props. name instead of assigning it directly to the state.Bind Events All in One PlaceIn the constructor, you can bind event handlers easily:constructor(props) {  super(props);  this.state = {    // Sets that initial state  };  // Our event handlers  this.onClick = this.onClick.bind(this);  this.onKeyUp = this.onKeyUp.bind(this);  // Rest Code }Avoid Assigning Values from this.props to this.stateIt might be tempting to set the component's state right away, but this could cause a few issues. One issue is that you can't really test it properly until the API call has been made and the response received. Another reason to avoid setting state in the constructor is that you don't need to worry about that value again once it's been defined.While this may seem the obvious approach, the constructor function is not always the right place to do API calls. If your component relies on another state that is available in its parent or grandparent components, then you may want to consider making API calls in componentDidMount(). This way you don't need to make API calls multiple times.constructor(props) {   super(props);     this.state = {    Reptile: 'Alligator',   }; }Do You Even Need a Constructor?React components have a useful feature as constructors. Constructors are difficult to manage. Don’t define the constructors if the state in the components would not be maintained. React applications are built using functional components and if state or event handlers are not required then it is better not to have the class components.Arrow FunctionsArrow functions make it possible to write more concise code, and they also help you to use the ‘this’ binding correctly. If you're using arrow functions, then you don't need to bind any event to 'this'. The scope of 'this' is global and not limited to any calling function.import React, { Component } from 'react'; class App extends Component {     constructor(props){       super(props);       this.state = {            data: 'ABC'         }     }     handleEvent = () => {       console.log(this.props);     }     render() {       return (         <div className="App">       <h2>React Constructor Example</h2>       <input type ="text" value={this.state.data} />           <button onClick={this.handleEvent}>Please Click</button>         </div>       );     }   }   export default App;The use of a constructor1) Initialization of the state constructorclass App extends Component {     constructor(props){           // here, it is setting initial value for 'inputTextValue'           this.state = {               inputTextValue: 'initial value',           };     }   }2) The way to use 'this' inside the constructorclass App extends Component {       constructor(props) {           // when you use 'this' in constructor, super() needs to be called first           super();           // it means, when you want to use 'this.props' in constructor, call it as below           super(props);       }   }3) Initialization of third-party librariesclass App extends Component {       constructor(props) {           this.myBook = new MyBookLibrary();          //Here, you can access props without using 'this'           this.Book2 = new MyBookLibrary(props.environment);       }   }4) Binding some context(this) when we need a class method to be passed in props to children.class App extends Component {     constructor(props) {            // when you need to 'bind' context to a function           this.handleFunction = this.handleFunction.bind(this);       }   }Example Program:React Component with Constructorindex.js  import React from 'react';  import ReactDOM from 'react-dom';  class Main extends React.Component {    constructor() {      super();      this.state = {        planet: "Earth"      }    }    render() {      return (        < h1 >Hello {this.state.planet}!</h1>      );    }  }  ReactDOM.render(<Main />, document.getElementById('root')); Output: Hello Earth! React Component without Constructor Index.js  import React from 'react';  import ReactDOM from 'react-dom';  class Main extends React.Component {    state = {      planet: "Mars"    }    render() {      return (        < h1 >Hello {this.state.planet}!</h1>      );    }  }  ReactDOM.render(<Main />, document.getElementById('root')); Output: Hello Mars! Constructor vs getInitialStateThe constructor and getInitialState in React are used to initialize state and they can’t be used interchangeably. The main fundamental difference between ES5 and ES6 is in the new class keyword. ES5 didn't provide the convenience of defining the React component as classes however ES did provide the convenience to define react component as class.  getInitialState is the ES5 friendly method to define the initial state of a React component. We use getInitialState with React.createClass and constructor is used with React.Component. For example class Goodmorning extends React.Component {    render() {      return <span>Good Morning</span>;    }  } It would rely on helper module called create-react-class:  var createGoodmorningReactClass = require('create-react-class');  var Goodmorning = createReactClass({    render: function() {      return <span>Good Morning</span>;    }  });  The object passed into create-react-class that is defined in initial stage by calling the getInitialState attribute:   var Goodmorning = createReactClass({    getInitialState: function() {      return {name: this.props.name};    },    render: function() {      return <span>Good {this.state.name}</span>;    }  });  In ES6 implementation:  class Goodmorning extends React.Component {    constructor(props) {      super(props);      this.state = {        name: props.name      }    }    render() {      return <span>Good {this.state.name}</span>;    }  } Does the Constructor Remain Relevant? React is an extremely powerful JavaScript Framework. Understanding how well its component lifecycle works would help to unlock the potential and power of the React JavaScript Framework.  As we have seen in this blog, as you build React components, the constructor is one of the features that isn’t supported in functions.  A constructor lets you define variables and initialize them with default values for the sake of convenience. However, if there is no state initialization or method binding, we do not need to define a constructor for a component in JavaScript. As illustrated in this case, we would not fetch data from the constructor and neither would binding methods be necessary to set the initial state. Like they say, it’s important to know the rules to know which ones can be broken. It’s a good method to learn about for when you might want to create several instances of a class with varying values for member functions.  

Understanding Constructors With React Components

2K
Understanding Constructors With React Components

The React Constructor is a method that’s automatically called during the creation of an object from a class. Simply put, the constructor, like its name, is a great tool to build things.

Constructors are used for two key objectives:

  • To initialize the local state of the component by assigning an object to this.state
  • To bind event handlers that occur in the component

In this blog, we’ll take you through all you need to understand about React constructors including the rules to be followed while implementing them. We will also look at how to bind events all in one place and take note of how to assign values accurately.

What is a Constructor?

In a class, a constructor is a method that is automatically called when an object of that class is created. Typically, this is how it works:

Syntax:

Constructor(props){ 
    super(props);   
}

A couple of points to note about a constructor are:

  1. It is not necessary to have a constructor in every component.
  2. It is necessary to call super() within the constructor. To set property or use 'this' inside the constructor it is mandatory to call super().

We must remember that the setState() method cannot be used directly in the constructor(). Use 'this.state' to assign the initial state in the constructor. The constructor uses this.state to assign initial state, and other methods should use set.state().

Call super(props) Before Using this.props

In React, the constructor is called during component creation and before mounting. If you want to implement the constructor for a React component, call the super(props) method before any other statement. Otherwise, this. props will be undefined in the constructor and create bugs.

constructor() { 
 console.log(this.props); 
}

Using super(props) is simple. We just have to call it in the constructor method of our child component:

constructor(props) {
 super(props);
 console.log(this.props);
}

Never Call setState() Inside constructor()

The constructor is the ideal place to set up your component's initial state. Instead of using setState() in other methods, you will need to assign the initial state directly.

class Hello extends React.Component { 
   constructor(props) { 
   super(props); 
   this.setState({ 
  title: 'This is the first test' 
   }); 
}   
  render() { 
    return <div>{this.state.title} </div> 
  } 
}   
ReactDOM.render(<Hello />, document.getElementById('container'));

When you use the setState() method in React, it does more than just assign a new value to this. state. It also re-renders the component and all its children. Additionally, if you are trying to update a class that was defined inside of a constructor, you will receive an error, so we should avoid setState() in constructors because it is the only place we directly assign the initial state to this.state.

constructor(props) { 
 super(props); 
 this.state = { 
   name 'kapil', 
   age: 22, 
 }; 
}

When creating a component, you should avoid setting values directly from the component's properties. Do it as follows:

constructor(props) {
 super(props);
 this.state = {
   name: props.name,
 };
}

If you try to change the name property in the state object, it will not work. If you want to modify this property later, you should not use setState(). Instead, access the name property directly in your code by using this.props. name instead of assigning it directly to the state.

Bind Events All in One Place

In the constructor, you can bind event handlers easily:

constructor(props) { 
 super(props); 
 this.state = { 
   // Sets that initial state 
 }; 
 // Our event handlers 
 this.onClick = this.onClick.bind(this); 
 this.onKeyUp = this.onKeyUp.bind(this); 
 // Rest Code 
}

Avoid Assigning Values from this.props to this.state

It might be tempting to set the component's state right away, but this could cause a few issues. One issue is that you can't really test it properly until the API call has been made and the response received. Another reason to avoid setting state in the constructor is that you don't need to worry about that value again once it's been defined.

While this may seem the obvious approach, the constructor function is not always the right place to do API calls. If your component relies on another state that is available in its parent or grandparent components, then you may want to consider making API calls in componentDidMount(). This way you don't need to make API calls multiple times.

constructor(props) { 
  super(props);   
  this.state = { 
   Reptile: 'Alligator', 
  }; 
}

Do You Even Need a Constructor?

React components have a useful feature as constructors. Constructors are difficult to manage. Don’t define the constructors if the state in the components would not be maintained. React applications are built using functional components and if state or event handlers are not required then it is better not to have the class components.

Arrow Functions

Arrow functions make it possible to write more concise code, and they also help you to use the ‘this’ binding correctly. If you're using arrow functions, then you don't need to bind any event to 'this'. The scope of 'this' is global and not limited to any calling function.

import React, { Component } from 'react';
class App extends Component {   
  constructor(props){   
    super(props);   
    this.state = {   
         data: 'ABC'   
      }   
  }   
  handleEvent = () => {   
    console.log(this.props);   
  }   
  render() {   
    return (   
      <div className="App">   
    <h2>React Constructor Example</h2>   
    <input type ="text" value={this.state.data} />   
        <button onClick={this.handleEvent}>Please Click</button>   
      </div>   
    );   
  }   
}   
export default App;

The use of a constructor

1) Initialization of the state constructor

class App extends Component {   
  constructor(props){   
        // here, it is setting initial value for 'inputTextValue'   
        this.state = {   
            inputTextValue: 'initial value',   
        };   
  }   
}

2) The way to use 'this' inside the constructor

class App extends Component {   
    constructor(props) {   
        // when you use 'this' in constructor, super() needs to be called first   
        super();   
        // it means, when you want to use 'this.props' in constructor, call it as below   
        super(props);   
    }   
}

3) Initialization of third-party libraries

class App extends Component {   
    constructor(props) {  
        this.myBook = new MyBookLibrary(); 
        //Here, you can access props without using 'this'   
        this.Book2 = new MyBookLibrary(props.environment);   
    }   
}

4) Binding some context(this) when we need a class method to be passed in props to children.

class App extends Component { 
    constructor(props) {   
        // when you need to 'bind' context to a function   
        this.handleFunction = this.handleFunction.bind(this);   
    }   
}

Example Program:

React Component with Constructor

index.js 
import React from 'react'; 
import ReactDOM from 'react-dom'; 
class Main extends React.Component { 
  constructor() { 
    super(); 
    this.state = { 
      planet: "Earth" 
    } 
  } 
  render() { 
    return ( 
      < h1 >Hello {this.state.planet}!</h1> 
    ); 
  } 
} 
ReactDOM.render(<Main />, document.getElementById('root')); 

Output: 

Hello Earth! 

React Component without Constructor 

Index.js 
import React from 'react'; 
import ReactDOM from 'react-dom'; 
class Main extends React.Component { 
  state = { 
    planet: "Mars" 
  } 
  render() { 
    return ( 
      < h1 >Hello {this.state.planet}!</h1> 
    ); 
  } 
} 
ReactDOM.render(<Main />, document.getElementById('root')); 

Output: 

Hello Mars! 

Constructor vs getInitialState

The constructor and getInitialState in React are used to initialize state and they can’t be used interchangeably. The main fundamental difference between ES5 and ES6 is in the new class keyword. ES5 didn't provide the convenience of defining the React component as classes however ES did provide the convenience to define react component as class 

getInitialState is the ES5 friendly method to define the initial state of a React component. We use getInitialState with React.createClass and constructor is used with React.Component. 

For example

 class Goodmorning extends React.Component { 
  render() { 
    return <span>Good Morning</span>; 
  } 
}
It would rely on helper module called create-react-class: 
var createGoodmorningReactClass = require('create-react-class'); 
var Goodmorning = createReactClass({ 
  render: function() { 
    return <span>Good Morning</span>; 
  } 
}); 
The object passed into create-react-class that is defined in initial stage by calling the getInitialState attribute: 
 var Goodmorning = createReactClass({ 
  getInitialState: function() { 
    return {name: this.props.name}; 
  }, 
  render: function() { 
    return <span>Good {this.state.name}</span>; 
  } 
}); 
In ES6 implementation: 
class Goodmorning extends React.Component { 
  constructor(props) { 
    super(props); 
    this.state = { 
      name: props.name 
    } 
  } 
  render() { 
    return <span>Good {this.state.name}</span>; 
  } 
} 

Does the Constructor Remain Relevant? 

React is an extremely powerful JavaScript Framework. Understanding how well its component lifecycle works would help to unlock the potential and power of the React JavaScript Framework.  

As we have seen in this blog, as you build React components, the constructor is one of the features that isnt supported in functions.  

A constructor lets you define variables and initialize them with default values for the sake of convenience. However, if there is no state initialization or method binding, we do not need to define a constructor for a component in JavaScriptAs illustrated in this case, we would not fetch data from the constructor and neither would binding methods be necessary to set the initial state. Like they say, it’s important to know the rules to know which ones can be broken. It’s a good method to learn about for when you might want to create several instances of a class with varying values for member functions.  

Rajesh

Rajesh Bhagia

Blog Author

Rajesh Bhagia is experienced campaigner in Lamp technologies and has 10 years of experience in Project Management. He has worked in Multinational companies and has handled small to very complex projects single-handedly. He started his career as Junior Programmer and has evolved in different positions including Project Manager of Projects in E-commerce Portals. Currently, he is handling one of the largest project in E-commerce Domain in MNC company which deals in nearly 9.5 million SKU's.

In his role as Project Manager at MNC company, Rajesh fosters an environment of teamwork and ensures that strategy is clearly defined while overseeing performance and maintaining morale. His strong communication and client service skills enhance his process-driven management philosophy.

Rajesh is a certified Zend Professional and has developed a flair for implementing PMP Knowledge Areas in daily work schedules. He has well understood the importance of these process and considers that using the knowledge Areas efficiently and correctly can turn projects to success. He also writes articles/blogs on Technology and Management

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Recently, GraphQL has made a lot of buzz among the developer community, and it has been receiving a lot of attention because of its dynamic nature along with its capability to fetch data, which is a lot less redundant. In this Code Tutorial, you will get to learn about what GraphQL really is, why has it created such hype amongst new-age developers, how is it different from the REST approach, and finally you will be building our own API with GraphQL along with Code Tutorials. Let’s get started!What is GraphQL? A quick primerBefore understanding what GraphQL is, let’s first understand what Query Languages are. Query Languages are computer languages that request the data from a database (called queries) to a client-side application through a server. A well-known example is Structured Query Language or SQL.Coming to GraphQL, by definition - “GraphQL is an open-source data query and manipulation language for APIs, and a runtime for fulfilling queries with existing data” (source: Wikipedia). Simply put, GraphQL is a new age Query Language developed by Facebook in 2012 that helps Application Programming Interfaces (APIs) fetch only that data which is requested by the client, and nothing else. This enormously reduces the redundant data at the API endpoint and making the requests blazing fast and developer friendly.Initially, GraphQL was an internal project of Facebook and it was created for fetching specific data and reducing network usage. In 2015, it was released publicly at the React.js conference and reference implementations and specifications of GraphQL in JavaScript were open-sourced. Later most of the programming languages adopted that. New languages like Python, Node.js, Java, C#, PHP, GO, and many more, support GraphQL.But wasn’t the same thing already being done by RESTful APIs? The answer is yes, but GraphQL is different than REST in a lot of ways.GraphQL is Client-Driven, whereas REST is Server-Driven.Queries are organized in terms of Schema and strict typecasting in GraphQL, whereas REST has Endpoints for that task.GraphQL calls Specific data with a single call. REST calls Fixed data with multiple calls.Instead of the GET, POST, PUT, DELETE operations in REST, GraphQL has Query, Mutation, and Subscription for data manipulation.Some of the other advantages of using GraphQL are:GraphQL is faster than other communication APIs.GraphQL can retreat multiple resources and results with a single request.It is easy to use complex systems and microservices with GraphQL as it unifies and hides their complexity.It offers multiple libraries and powerful tools for various projects such as GraphiQL, GraphQL Explorer, Apollo.No under and over data fetching. It fetches the amount of data that is required.The core building block of GraphQL is its schema which is used as a middle way between server and client while defining the accessibility of the data.  A GraphQL schema is written in Schema Definition Language (SDL) and refers to the exact mutations and queries that a client can execute against your data graph. It can be built with any programming language. Simply, the schema defines the type of data that can be fetched, the relationships between these types of data, and what type of queries are allowed. The most basic components of a GraphQL schema are object types. They represent a kind of object you can fetch from your service along with the fields it has. Further, schema helps the client validate their query and eliminate unavailable data or the wrong structure stage.The other two fundamental parts of GraphQL are Query and Resolver. The request to fetch a particular data is called a query and a resolver is used to tell the server from where and how to fetch the data corresponding to the given field. You can execute the GraphQL queries either by Command line or by using a GraphQL server.GraphQL works in three parts – a query to read data, a mutation to write data, and a subscription to receive real-time data over time.Now that you know the ‘What’ and ‘Where’of GraphQL, let’s dive straight into our favorite part, the development phase.Let’s Play with GraphQLTo get started with GraphQL, you need a server that serves your API and a client that connects to your service endpoints. In this section, you will learn about a step-by-step procedure of building an API using GraphQL and Express on top of Node.js. In the next section, you will be implementing these prerequisites into code and start our development for the API.Prerequisites:Understanding of GraphQLNode Package Manager (or NPM) with version 10+Knowledge of basic querying and server-side programming.We will be needing a database to store the user data and everything else that a client-side application can request for. For this, you will be using LowDB, which is a simple file based JSON database for small projects in the localhost. Then you will be needing middleware to connect our database system to the requesting frontend application. For this, you will be using the Express middleware with the GraphQL implementation of Express - the Graphql-express library. Finally, you will be making a client-side application using react which can request all the data from the local database and can perform operations on the database like read, write, and delete.So, our roadmap is simple and straightforward. Create a Database Schema > Use a middleware server to query the database > Create a frontend application to use the data. If this is too much at once for you, do not worry as this is article is being written keeping in mind that the reader is a first-timer for GraphQL and basic querying as usual. Now, let’s dive into the code.Setting up Express GraphQLLet’s begin with the basic project structure of a Node.js application. Begin a new project in a new folder.$ mkdir graphql-example $ cd graphql-exampleUse NPM to intiialize a project$ npm init -yInstall the required dependencies for Express, MongoDB (Mongoose), and some additional dependencies required for the function of Express.$ npm install express mongoose body-parser cors --saveApollo Server is a community-maintained open-source GraphQL server that works with all Node.js HTTP server frameworks, so next, you are going to download and save that.$ npm install apollo-server-express --saveThis should’ve created a package.json and a package-lock.json file within your folder. These files contain information regarding our environment, the dependencies, and the specific versions to run those dependencies.This means our environment is ready and you can now start developing the integrated server and API. We are going to write the Schema inside the index.js file. In the index.js file, start off by writing this code.const express = require('express'); const mongoose = require('mongoose'); const schema = require('./schema'); const bodyParser = require('body-parser'); const cors = require('cors'); const { ApolloServer } = require('apollo-server-express'); const url = "mongodb://localhost:27017/moviesdb"; const connect = mongoose.connect(url, { useNewUrlParser: true }); connect.then((db) => {       console.log('Connected correctly to server!'); }, (err) => {       console.log(err); }); const server = new ApolloServer({       typeDefs: schema.typeDefs,       resolvers: schema.resolvers }); const app = express(); app.use(bodyParser.json()); app.use('*', cors()); server.applyMiddleware({ app }); app.listen({ port: 4000 }, () =>   console.log(`Server ready at  http://localhost:4000${server.graphqlPath}`));In lines number 1 to 6, you’re implementing the necessary modules. Note that here you have imported the ./schema, but you haven’t created that yet. We will be doing this in the next step.In lines number 9 to 14, you are connecting the project to the MongoDB database and logging any error you face to the console.In lines number 16 to 19, you’re creating a new Apollo Server with typeDefs and Resolver. We’ll be defining those in the ./schema later in this tutorial.In lines 21 to 26, you’re firing up the Express Server at port 4000, when you will actually be able to interact with what you’re building.GraphQL has two main principles to work: types and resolvers. We defined them in Apollo Server. We’ll import them from the file you’ll create later.Next, let’s create the file models/movie.js that’ll contain the movie-Mongoose model.const mongoose = require('mongoose'); const Schema = mongoose.Schema; const movieSchema = new Schema({     name: {        type: String,        required: true     },     rating: {        type: Number,        required: true     },     producer: {        type: String,        required: true    } }, {     timestamps: true }); var Movies = mongoose.model('Movie', movieSchema); module.exports = {Movies, movieSchema};We’re going to build a simple movie app, where you can show, add, edit, and delete movies. That way you’ll get through the basics of GraphQL, which is the main goal of this tutorial.In lines 4 to 19, you’re basically determining the schema of the database that is going to hold the data of movies. Every movie is going to have a Name and a Producer of type String and a Rating of type Number.Designing the SchemaLet’s move on to the schema.js file where you’re going to build our GraphQL API.Create a new file in the root of the folder by the name of schema.js and add the following code.const { gql } = require('apollo-server-express');   const Movie = require('./models/movie').Movies;   const typeDefs = gql `    type Movie {      id: ID!      name: String!      producer: String!      rating: Float!  }  type Query {    getMovies: [Movie]    getMovie(id: ID!): Movie  }  type Mutation {      addMovie(name: String!, producer: String!, rating: Float!): Movie      updateMovie(id: ID!, name: String!, producer: String!, rating: Float): Movie      deleteMovie(id: ID!): Movie    } `In this, you’re building the schema. We defined the Movie type which will have an ID, the name of the movie and the producer, and a rating of type Float. The “!” after the types shows that these fields are necessary.Unlike the REST approach of getting different tasks done at different endpoint URLs, GraphQL can create operations in a single endpoint. That is what you have done in line 11 onwards. The type Query determines the GET operations, and type Mutation determines the modification operations like POST, DELETE, etc. In getMovies, you’re returning a list of all available movies in our database, and in getMovie, you’re getting the specific movie by the ID of that movie.Now you’re going to link these with the Mongoose Database queries that are going to perform the actions in the database. And this is done by Resolvers. Resolvers are a collection of functions that connect schema fields and types to various backends. It can read, write, and delete data from and to anywhere in the database, be it SQL, NoSQL, or Graph-based database. In simple terms, they act as a GraphQL query handler. Here’s how you’re going to implement Resolvers in our code:const resolvers = {   Query: {     getMovies: (parent, args) => {       return Movie.find({});     },     getMovie: (parent, args) => {       return Movie.findById(args.id);     }   },   Mutation: {     addMovie: (parent, args) => {       let movie = new Movie({         name: args.name,         producer: args.producer,         rating: args.rating,       });       return movie.save();     },     updateMovie: (parent, args) => {       if (!args.id) return;         return Movie.findOneAndUpdate(          {            _id: args.id          },          {            $set: {              name: args.name,              producer: args.producer,              rating: args.rating,            }          }, {new: true}, (err, Movie) => {            if (err) {              console.log('Something went wrong when updating the movie');            } else {              continue;            }          }       );     }   } } module.exports = {typeDefs,resolvers};This is the basic logic of MongoDB and CRUD applications, which doesn’t come under the scope of this article, since it is majorly focused on GraphQL. However, the logic is simple and straightforward for anyone to understand, so skim through it once.With this, you’re done with a basic Movie API that can perform all the CRUD operations on a database of movies. To test this out, you’re going to fire up our node server and open the browser in http://localhost:4000/graphql which will open the GraphQL Playground.$ node index.js Server ready at http://localhost:4000/graphqlOnce the Playground UI opens, you’re first going to create a Movie Record for the database since it would initially be empty.mutation { addMovie(name: “GraphQL Movie”, producer: “Facebook”, rating:  4.5) { id, name, rating, producer } }OUTPUT:{ “data” : { “addMovie”: { “id”: “5j2j1lnk1LNS231MLK3”, “name”: “GraphQL Movie”, “producer”: “Facebook”, “rating”: 4.5 } } }And now let’s list out all the movies in the database with only their “name” and “rating”.query { getMovies: { name, rating } }OUTPUT:{ “Data”: { “getMovies”: [ { “name”: “GraphQL Movie”, “rating”: 4.5 } ] } }So, you have successfully created a Movie API where you can perform all the CRUD operations on a single endpoint, and also ask for just the data that you want.  This results in a blazing fast API response and a developer-friendly return object that makes development fast and easy.Using GraphQL with ReactUsing GraphQL with react is super easy and can make full-stack development look like a piece of cake. We’re going to build a react app that uses the Movie API you just built to render the results on a frontend client app.Start off by installing the required dependencies.$ npm install create-react-app graphql @apollo/clientCreate a new React appnpx create-react-app movies-appLet’s start off by initializing an ApolloClient instance. In index.js let's first import the symbols you need from @apollo/client, Next, you'll initialize ApolloClient, passing its constructor a configuration object with URI and cache fields:import {   ApolloClient,   InMemoryCache,   ApolloProvider,   useQuery,   gql } from "@apollo/client"; const client = new ApolloClient({   uri: 'https://48p1r2roz4.sse.codesandbox.io',   cache: new InMemoryCache() });The URI specifies the GraphQL Server URL.That’s it! Our client app is ready to fetch data from the GraphQL server. In index.js, let’s wrap our React app with the ApolloProvider Component. Put up the ApolloProvider somewhere high in the app, above any component that might need to access GraphQL data.function App() {   return (           My first GraphQL app       ); } render(         ,   document.getElementById('root'), );With this being done, our client app is now ready to request data from the server and perform queries on the frontend. We can do this using the useQuery React Hook that shares the GraphQL data with the UI.In the index.js, let’s first define the query you want to execute.const MOVIES = gql`   query getMovies {      name,      producer   } `;Next, let's define a component called GetMovies that executes our getMovies query with the useQuery hook:function GetMovies() {   const { loading, error, data } = useQuery(MOVIES);   if (loading) return Loading...;   if (error) return Error :(;   return data.map(({ name, producer }) => (                   {name}: Produced by {producer}             )); }Whenever this component renders, the useQuery hook automatically executes our query and binds the results to the data property on successful completion of the query.Finally, you'll add GetMovies to our existing component tree:function App() {   return (           My first Apollo app             ); }When your app reloads, you should briefly see a loading indicator, followed by a list of Movies present in the MongoDB database.Congratulations. You just made a React app that uses GraphQL to render data from the server. Give yourself a pat on the back for this one.Dev-friendly Query Languages are the FutureSo, wrapping it all up in a few more lines. In this tutorial, you learned what GraphQL is - a new age Query Language that is data specific and client-oriented, how is it different (and better) than REST architecture - it is developer friendly, blazing-fast, and easy to learn or understand. We also made a mock API of Movies using GraphQL and MongoDB and performed the CRUD operations using just one single endpoint URL - another benefit over the RESTful architecture. And finally, you went on to create a React application that uses these benefits of GraphQL and combines them with the benefits of React to give a hyper-fast, easy, and full-stack app that renders Movies on request.We hope you learned something new from this article. Once you’ve started this journey of GraphQL, it is a fun ride ahead since it is a relatively new tech and not many people out there are having this skill under their hood. So, make use of this opportunity and outshine the rest.Keep Learning.
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Create GraphQL API with example

Recently, GraphQL has made a lot of buzz among the... Read More

How to use Timers in Node.js

You can use Node.js's utilities to schedule the execution of your code. The timer module, unlike most Node.js modules, is not imported. To comply with the JavaScript browser API, the methods are globally accessible.The Node.js Timers module contains several functions that allow you to execute a block of code or a function after a specified amount of time. You don't need to use require() to import the Timers module because it's global.In this post, I'll explain and demonstrate what timers are, how to use them, how the syntax looks, and how you can use them in your applications. For example, if you want to retrieve data from a REST API at a specific interval, you can easily do so with timers. So, even if you are unfamiliar with JavaScript or timers, this post will help you understand these concepts.The Event Loop - A Quick PrimerNode.js is a single-threaded, event-driven platform that can run non-blocking, asynchronous code. These Node.js features make it memory efficient. Even though JavaScript is single-threaded, the event loop enables Node.js to perform non-blocking I/O operations. It is accomplished by delegating tasks to the operating system whenever and wherever possible.Because most operating systems are multi-threaded, they can handle multiple operations that are running in the background. When one of these operations is finished, the kernel notifies Node.js, and the callback associated with that operation is added to the event queue, where it will eventually be executed.Features of Event Loop:An event loop is an infinite loop that waits for tasks, executes them, and then sleeps until more tasks are received.When the call stack is empty, i.e., there are no ongoing tasks, the event loop executes tasks from the event queue.We can use callbacks and promises in the event loop.The event loop executes the tasks in reverse order, beginning with the oldest.Example:console.log("One"); setTimeout(function(){ console.log("Two"); }, 1000); console.log("Three");Output:OneThreeTwoThe first console log statement is pushed to the call stack in the above example, and "One" is logged on the console before the task is popped from the stack. Following that, the setTimeout is added to the queue, the task is sent to the operating system, and the task's timer is set. After that, this task is removed from the stack. The third console log statement is then pushed to the call stack, "Three" is logged on the console, and the task is removed from the stack.Timers in JavaScriptA timer is used in JavaScript to execute a task or function at a specific time. The timer is essentially used to delay the execution of the program or to execute the JavaScript code at regular intervals. You can delay the execution of the code by using a timer. As a result, when an event occurs or a page loads, the code does not complete its execution at the same time.Advertisement banners on websites, which change every 2-3 seconds, are the best example of a timer. These advertising banners are rotated at regular intervals on websites such as Flipkart. To change them, you set a time interval.JavaScript provides two timer functions, setInterval() and setTimeout(), which help to delay code execution and allow one or more operations to be performed repeatedly.setTimeout():The setTimeout() function allows users to postpone the execution of code. The setTimeout() method accepts two parameters, one of which is a user-defined function, and the other is a time parameter to delay execution. The time parameter, which is optional to pass, stores the time in milliseconds (1 second = 1000 milliseconds).setInterval():The setInterval method is similar to the setTimeout() function in some ways. It repeats the specified function after a time interval. Alternatively, you can say that a function is executed repeatedly after a certain amount of time specified by the user in this function.Timers in Node.js - setTimeout()setTimeout() can be used to execute code after a specified number of milliseconds. This function is equivalent to window. setTimeout() from the browser JavaScript API, but no code string can be passed to be executed.setTimeout() takes a function to execute as the first argument and a millisecond delay defined as a number as the second. Additional arguments may be provided, and these will be passed to the function. As an example, consider the following:Using setTimeout()The timeout interval is not guaranteed to execute after that exact number of milliseconds. This is because any other code that blocks or holds onto the event loop will delay the execution of the timeout. The only guarantee is that the timeout will not be executed sooner than the timeout interval specified.setTimeout(function A() { return console.log('Hello World!'); }, 2000); console.log('Executed before A');clearTimeout():The clearTimeout() method deactivates a timer that was previously set with the setTimeout() method.The ID value returned by setTimeout() is passed to the clearTimeout() method as a parameter.Syntax:clearTimeout(id_of_settimeout)Example: function welcome () { console.log("Welcome to Knowledgehut!"); } var id1 = setTimeout(welcome,1000); var id2 = setInterval(welcome,1000); clearTimeout(id1);Timers in Node.js - setImmediate()To execute code at the end of the loop cycle, use the setImmediate() method. In layman's terms, this method divides tasks that take longer to complete, in order to run a callback function that is triggered by other operations such as events.Syntax:let immediateId = setImmediate(callbackFunction, [param1, param2, ...]); let immediateId = setImmediate(callbackFunction);The function to be executed will be the first argument to setImmediate(). When the function is executed, any additional arguments will be passed to it.Now consider the difference between setImmediate() and process. nextTick(), as well as when to use which.While processing, setImmediate() is executed in the Check handlers phase. process.nextTick() is called at the start of the event loop and at the end of each phase.process.nextTick() has higher priority than setImmediate():setImmediate(() => console.log('I run immediately')) process.nextTick(() => console.log('But I run before that'))Output:Using setImmediate()Multiple setImmediate functions are called in the following example. When you do this, the callback functions are queued for execution in the order in which they are created. After each event loop iteration, the entire callback queue is processed. If an immediate timer is queued from within an executing callback, it will not be triggered until the next iteration of the event loop.Example:setImmediate(function A() { setImmediate(function B() { console.log(1); setImmediate(function D() {   console.log(2); }); }); setImmediate(function C() { console.log(3); setImmediate(function E() {   console.log(4); }); }); }); console.log('Started');clearImmediate():The clearImmediate function is used to remove the function call that was scheduled by the setImmediate function. Both of these functions can be found in Node.js's Timers module.Example:console.log("Before the setImmediate call") let timerID = setImmediate(() => {console.log("Hello, World")}); console.log("After the setImmediate call") clearImmediate(timerID);Timers in Node.js - setInterval()This method, unlike setTimeout(), is used to execute code multiple times. For example, the company may send out weekly newsletters to its Edge as a Service customer. This is where the setInterval() method comes into play. It is an infinite loop that will continue to execute as long as it is not terminated (or halted).As the second argument, setInterval() accepts a function argument that will run an infinite number of times with a given millisecond delay. In the same way that setTimeout() accepts additional arguments beyond the delay, these will be passed on to the function call. The delay, like setTimeout(), cannot be guaranteed due to operations that may stay in the event loop and should thus be treated as an approximation.Syntax:let intervalId = setInterval(callbackFunction, [delay, argument1, argument2, ...]); //option 1 let intervalId = setInterval(callbackFunction[, delayDuration]); // option 2 let intervalId = setInterval(code, [delayDuration]); //option 3Using setInterval()Example:setInterval(function A() { return console.log('Hello World!'); }, 1000); // Executed right away console.log('Executed before A');setInterval(), like setTimeout() returns a Timeout object that can be used to reference and modify the interval that was set.In the above example, function A() will execute after every 1000 milliseconds.clearInterval():Example:var si = setInterval(function A() { return console.log("Hello World!"); }, 1000); setTimeout(function() { clearInterval(si); }, 4000);Using Timer.unref()The timer module is used to schedule functions that will be called later. Because it is a global API, there is no need to import (require("timers")) to use it.The Timeout Class contains an object (setTimeout()/setInterval()) that is created internally to schedule actions, and (clearTimeout()/clearInterval()) that can be passed to cancel those scheduled actions. When a timeout is set, the Node.js event loop will continue to run until clearTimeout() is called. The setTimeout() method returns timeout objects that can be used to control this default behaviour, and it exports both the timeout.ref() and timeout.unref() functions.timeout.ref():When the Timeout is active and (timeout.ref()) is called, it requests that the Node.js event loop not exit for an extended period of time. In any case, calling this Method multiple times has no effect.Syntax:timeout.ref()timeout.unref():When the Timeout is enabled, the Node.js event loop is not required to remain active. If any other activity keeps the event loop running, the Timeout object's callback is invoked after the process exits. In any case, calling this Method multiple times has no effect.Syntax:timeout.unref()Example:var Timeout = setTimeout(function alfa() { console.log("0.> Setting Timeout", 12); }); console.log("1 =>", Timeout.ref()); Timeout.unref() Timeout.ref() console.log("2 =>", Timeout.unref()); clearTimeout(Timeout); console.log("3 => Printing after clearing Timeout"); Output:Scheduling Made SimplerIn this tutorial, you learned how to schedule tasks with the Node.js timer module. You've seen how to set timeouts, interval timers for recurring tasks, and how to use set immediate to bypass long operations. You've also seen how to stop these operations using the clear() method for each method.As with learning anything new, practising what you learn will make a big difference to how easily you can perform these tasks. Share your thoughts and questions in the comments as you try out what you’ve learnt.
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How to use Timers in Node.js

You can use Node.js's utilities to schedule the ex... Read More