Search

What Are React.Js Prop

Understanding data manipulation in React is never an easy job. React has a unidirectional data flow due to which the technique of data manipulation in React is slightly different than in other frameworks.   To understand the concepts like Props or State, I’d recommend you brush up or go through the data flow concepts in React first. In this article, we’re going to focus only on the Props feature and how to use it in React. We already know that components are reusable, and we can use our component multiple times in our application. To understand props, you should have a solid understanding of the components and how data flows inside the components.  If you don’t know much about React components, I recommend you stop here and read about React components first before continuing! Let’s now learn what are “props” and how to use them?What is Props in React?   We all know that React Components allow you to split the application interfaces into reusable, independent segments.  “Props” stands for properties. It is a special keyword in React which is used for passing data from one component to another.   Logically, components are just like JavaScript functions. They accept random inputs (called “props”) and return React elements which tell what should be displayed on the screen.   Props can be used to pass any kind of data such as:  String Array Integer Boolean Objects or, Functions Understanding ReactJS Props   We are all quite familiar with parent and child components. If you aren’t, then before delving deep into ReactJS props, it’s important to revisit concepts on parent and child components.class ParentComponent extends Component {   render() {    return (      < h1 >        I'm the big parent component.        <ChildComponent />      </ h1 >    ); } }And here is the child component:const ChildComponent = () => {   return <p>I'm a small child!</p> };And did you realize that when we called the child component inside the parent component, we end up rendering the same data again and again? The problem we want to solve here is, we want to render the dynamic data and not static data! Let’s understand this with a simple example. Here we have two components:     One is the parent component which is a class component://this is Parent component import React, { Component } from 'react'; import MyComponent from './MyComponent.jsx'; class App extends Component {    render() {        return (            <div>                <MyComponent />                <MyComponent />            < /div>        );    } } export default App;And we are rendering the child component ( MyComponent ) which is a functional component inside the parent as follows:import React from 'react'; const MyComponent = () => {    return < h1 > Hello Michael </h1> } export default MyComponent;The result will be like this:Hello Michael Hello MichaelThis is coming twice, because we have used <MyComponent> twice in our parent component. We can re-use this component any ‘n’ number of times as we want. Now, what if a certain scenario demands that we don’t require this static data in the child component, and we want some dynamic data when the component renders? What I meant is that I want to reuse the child component not with the data it has, but with some other data like:Hello Michael Hello ProfessorHere we can make use of Props or properties. We can add props in the component in the same way that we add attributes in our HTML.Let’s add Props in our older component and see the results:  import React, { Component } from 'react';  import MyComponent from './MyComponent.jsx';  class App extends Component {     render() {         return (             <div>                 <MyComponent name = "Michael" />                 <MyComponent name = "Professor" />             </div>         );     }  }  export default App;  In the above file, we have used a name attribute with the desired dynamic value we want after rendering the data. Now, the most important point here is to pass props to the child component.Passing Props >>>>>  import React from 'react';  const MyComponent = (props) => {     return < h1 > {props.name} </ h1>  }  export default MyComponent;  If you try to console the value of Props, you will see nothing but a plain JavaScript object with key-value pairs. We can access the value as key of “name” using (.) dot notation like this >>> “props.name“,  In the final step, we have used interpolation to use the props and we enclose it in curly brackets because it is a JSX expression.  Now after calling the child component inside the parent component, here comes the desired output which isHello Michael  Hello Professor Now that we’ve successfully rendered the data of the child component from the parent component, let’s dig deeper!Props in the Constructor:In the above example, we have used a functional component.   What if we have a class component and we want to use props in that component?  Normally, a constructor() method is invoked when a class in a component is created without using the newer public class fields syntax. Most of the times when a constructor() is invoked, the super() method is invoked inside of it. Otherwise, the parent’s constructor will not be executed.  See the snippet below for the class component:  class MyComponent extends React.Component {     constructor(props) {         super(props);         console.log(this.props); // props will be logged here.     }     render() {         return < h1 >Hello {this.props.name}</h1>;    }  }  To access the props we use this.props.  To summarize the above: If we want to use this.props inside the constructor, we need to pass it in super, or else we can use it in render() without using super()  Using Props in React & Passing Data using Props  Props are mainly used for passing data from the parent component to child component. It motivates us to reuse the components and reduce redundancy as well. But as a growing app, you might see a lot of bugs with typechecking.  In React there is a special inbuilt feature that is used to check the basic validations during typechecking using PropTypes.  See the depth and power of propTypes here:  import PropTypes from 'prop-types'  export default class Mycomponent extends React.Component {     render() {         // .... Your code goes here     }  }  Heading.propTypes = {     content: PropTypes.string.isRequired,     message: PropTypes.array.isRequired,     onClick: PropTypes.func.isRequired,     length: PropTypes.number.isRequired,     styles: PropTypes.object.isRequired,     isReady: PropTypes.bool.isRequired  } PropTypes, a built-in-type checker, ensures that the right type of props is passed to a component. We can define components without propTypes as well, but why risk our application with any wrong data type that might lead to a crash?  NOTE: propTypes can only be checked in development mode (for performance reasons) PROPTYPES exports a huge range of validators which can be used to make sure that the data you receive is checked and valid, completely bug free!   To use typechecking on the props for a component, let’s use and assign the special propTypes property as follows:   import PropTypes from 'prop-types';  class MyComponent extends React.Component {     render() {         return (             < h1 >Hello, {this.props.name}</h1>         );     }  }    MyComponent.propTypes = {     name: PropTypes.string  };  In this example, we have used “PropTypes.string”. When an invalid value is provided for a prop, for-ex, other than a string, a warning will be thrown in the JavaScript console. To learn more about prop types, head over here.   Default PropsThere could be certain scenarios in which we need some default props so that props are set even if a parent component doesn’t pass the props down. In this case, we can also define default values for the props directly to the constructor by assigning to the special property known as defaultProps provided by React.  class MyComponent extends React.Component {     render() {         return (             < h1 >Here comes the, {this.props.name}</h1>         );     }  }    // Specifies the default values for props:  MyComponent.defaultProps = {     name: 'new value'  };    // Renders "Here comes, new value":  ReactDOM.render(     <MyComponent />,     document.getElementById('dummy')  );        Default props work great in the situation when the same default value can be utilized again and again for every instance of the component. Again reduce the LOC (line of code).  Why are Props useful?  Props provide a medium so that components can talk to each other.  In fact, we can reduce thousands of lines of code just by using Props!     Whenever we declare any component it can be either a class component or a functional component. One thing to notice here is, no matter what kind of component is, it should never change its props value.      Hence the components should act like pure functions (which can’t change their own input) to their props.     But, if you really want to change or introduce some dynamic UIs that should change within the component, you should learn about “State”.     State allows React components to change their values over time without any violations. A state is usually called as an encapsulated one or having a local scope of the component.     It is not accessible to any component other than the one that owns it and sets it.     You can learn about the state in this article.     Can we use Props and State Together?   Absolutely  ! Let’s understand with the following example how we can combine both state and props in our component.    import React from 'react';    class App extends React.Component {     constructor(props) {         super(props);         this.state = {             heading: "Heading from props...",             content: "Some Content from props..."   //Line-8         }     }     render() {        //Line-11         return (             <div>                 <Header headingProp={this.state.heading} />                 <Content contentProp={this.state.content} />             </div>         );     }  }  class Header extends React.Component {     render() {         return (             <div>                 < h1 >{this.props.headingProp}</h1>             </div>         );     }  }  class Content extends React.Component {     render() {         return (             <div>                 < h2 >{this.props.contentProp}</h2>             </div>         );     }  }  export default App;          An explanation for the above snippet:  Here we have initialized and used the state in our parent component (line number 7-8) and we have used that state by passing it down the component tree using props.   Inside the render() (line number 11), we are setting the props data as headerProp and contentProp used in child components which are <Header> component and <Content> component.   Now, if you change the state in the parent component, all the child components get updated, because the single source pf data is State here!    What are the differences between props and state?  Let’s  take a look at some high-level differences between state and props. Although they do similar things, they are used differently.   While both are used for data manipulation, one is of private and the other is of dynamic context.      Props are used to pass data from parent to child whereas the state is used for data manipulation inside the component.  We can get the value of props from the parent component, where we get the value of state object from the initial data defined in the constructor() method.  While this.props is set up by React itself, with this.state we are free to add additional fields to the component manually to store something or in a scenario that doesn’t participate in the data flow.   Props are immutable, i.e We can't change props passed to a component whereas we can change the State, i.e React uses the setState() method to update the object of a state (but within the component itself) Conclusion    Props is a very crucial concept while learning React. In this article, you have learned about the lifeline of React, which is Props, and how we can use props in React. You have got clarity on why a component updates or re-renders when data in the props changes. We also saw that whenever data changes in props, the component will re-render. Last but not the least, let’s just recall the pointers of all of the above: Props are like parameters to a function  Props cannot be changed, they are immutable  A prop is a special keyword in React, that stands for properties  Props can only be passed in a uni-direction i.e (parent to child)  Props can be used to pass dynamic data to a component A component re-renders when data in the props changeHope you find this article useful! Happy Learning!      

What Are React.Js Prop

10K
What Are React.Js Prop

Understanding data manipulation in React is never an easy job. React has a unidirectional data flow due to which the technique of data manipulation in React is slightly different than in other frameworks.   

To understand the concepts like Props or State, I’d recommend you brush up or go through the data flow concepts in React first. 

In this article, we’re going to focus only on the Props feature and how to use it in React. 

We already know that components are reusable, and we can use our component multiple times in our application. To understand props, you should have a solid understanding of the components and how data flows inside the components.  

If you don’t know much about React components, I recommend you stop here and read about React components first before continuing! 

Let’s now learn what are “props” and how to use them?

What is Props in React?   

We all know that React Components allow you to split the application interfaces into reusable, independent segments.
 
“Props” stands for properties. It is a special keyword in React which is used for passing data from one component to another.
 
Logically, components are just like JavaScript functions. They accept random inputs (called “props”) and return React elements which tell what should be displayed on the screen.   


Props can be used to pass any kind of data such as:  

  • String
  • Array
  • Integer
  • Boolean
  • Objects or,
  • Functions 

Understanding ReactJS Props   

We are all quite familiar with parent and child components.

If you aren’t, then before delving deep into 
ReactJS props, it’s important to revisit concepts on parent and child components.

class ParentComponent extends Component {   
render() { 
   return ( 
     < h1 > 
       I'm the big parent component. 
       <ChildComponent /> 
     </ h1 > 
   ); 
} 
}

And here is the child component:

const ChildComponent = () => {   
return <p>I'm a small child!</p>
};

And did you realize that when we called the child component inside the parent component, we end up rendering the same data again and again?

The problem we want to solve here is, we want to render the dynamic data and not static data!

Let’s understand this with a simple example. Here we have two components:    

One is the parent component which is a class component:

//this is Parent component 

import React, { Component } from 'react'; 
import MyComponent from './MyComponent.jsx'; 
class App extends Component { 
   render() { 
       return ( 
           <div> 
               <MyComponent /> 
               <MyComponent /> 
           < /div> 
       ); 
   } 
} 
export default App;

And we are rendering the child component ( MyComponent ) which is a functional component inside the parent as follows:

import React from 'react'; 
const MyComponent = () => { 
   return < h1 > Hello Michael </h1> 
} 
export default MyComponent;

The result will be like this:

Hello Michael 
Hello Michael

This is coming twice, because we have used <MyComponent> twice in our parent component. We can re-use this component any ‘n’ number of times as we want.

Now, what if a certain scenario demands that we don’t require this static data in the child component, and we want some dynamic data when the component renders? What I meant is that I want to reuse the child component not with the data it has, but with some other data like:

Hello Michael 
Hello Professor

Here we can make use of Props or properties. We can add props in the component in the same way that we add attributes in our HTML.

Let’s add Props in our older component and see the results:  

import React, { Component } from 'react'; 
import MyComponent from './MyComponent.jsx'; 
class App extends Component { 
   render() { 
       return ( 
           <div> 
               <MyComponent name = "Michael" /> 
               <MyComponent name = "Professor" /> 
           </div> 
       ); 
   } 
} 
export default App;  

In the above file, we have used a name attribute with the desired dynamic value we want after rendering the data. Now, the most important point here is to pass props to the child component.

Passing Props >>>>>  

import React from 'react'; 
const MyComponent = (props) => { 
   return < h1 > {props.name} </ h1> 
} 
export default MyComponent;  

If you try to console the value of Props, you will see nothing but a plain JavaScript object with key-value pairs. We can access the value as key of “name” using (.) dot notation like this >>> “props.name“,  

In the final step, we have used interpolation to use the props and we enclose it in curly brackets because it is a JSX expression.  

Now after calling the child component inside the parent component, here comes the desired output which is

Hello Michael 
Hello Professor 

Now that we’ve successfully rendered the data of the child component from the parent component, let’s dig deeper!

Props in the Constructor:

In the above example, we have used a functional component.   

What if we have a class component and we want to use props in that component?  

Normally, a constructor() method is invoked when a class in a component is created without using the newer public class fields syntax. Most of the times when a constructor() is invoked, the super() method is invoked inside of it. Otherwise, the parent’s constructor will not be executed.  

See the snippet below for the class component:  

class MyComponent extends React.Component { 
   constructor(props) { 
       super(props); 
       console.log(this.props); // props will be logged here. 
   } 
   render() { 
       return < h1 >Hello {this.props.name}</h1>;    } 
}  

To access the props we use this.props.  

To summarize the above: If we want to use this.props inside the constructor, we need to pass it in super, or else we can use it in render() without using super()  

Using Props in React & Passing Data using Props  

Props are mainly used for passing data from the parent component to child component. It motivates us to reuse the components and reduce redundancy as well. But as a growing app, you might see a lot of bugs with typechecking.  

In React there is a special inbuilt feature that is used to check the basic validations during typechecking using PropTypes.  

See the depth and power of propTypes here:  

import PropTypes from 'prop-types' 
export default class Mycomponent extends React.Component { 
   render() { 
       // .... Your code goes here 
   } 
} 
Heading.propTypes = { 
   content: PropTypes.string.isRequired, 
   message: PropTypes.array.isRequired, 
   onClickPropTypes.func.isRequired, 
   length: PropTypes.number.isRequired, 
   styles: PropTypes.object.isRequired, 
   isReadyPropTypes.bool.isRequired 
} 

PropTypes, a built-in-type checker, ensures that the right type of props is passed to a component. We can define components without propTypes as well, but why risk our application with any wrong data type that might lead to a crash?  

NOTE: propTypes can only be checked in development mode (for performance reasons) 

PROPTYPES exports a huge range of validators which can be used to make sure that the data you receive is checked and valid, completely bug free!   

To use typechecking on the props for a component, let’s use and assign the special propTypes property as follows:   

import PropTypes from 'prop-types'; 
class MyComponent extends React.Component { 
   render() { 
       return ( 
           < h1 >Hello, {this.props.name}</h1> 
       ); 
   } 
} 
 
MyComponent.propTypes = { 
   name: PropTypes.string 
};  

In this example, we have used “PropTypes.string”. When an invalid value is provided for a prop, for-ex, other than a string, a warning will be thrown in the JavaScript console. To learn more about prop types, head over here  

Default Props

There could be certain scenarios in which we need some default props so that props are set even if a parent component doesn’t pass the props down. 

In this case, we can also define default values for the props directly to the constructor by assigning to the special property known as defaultProps provided by React.  

class MyComponent extends React.Component { 
   render() { 
       return ( 
           < h1 >Here comes the, {this.props.name}</h1> 
       ); 
   } 
} 
 
// Specifies the default values for props: 
MyComponent.defaultProps = { 
   name: 'new value' 
}; 
 
// Renders "Here comes, new value": 
ReactDOM.render( 
   <MyComponent />, 
   document.getElementById('dummy') 
);       

Default props work great in the situation when the same default value can be utilized again and again for every instance of the component. Again reduce the LOC (line of code).  

Why are Props useful?  

Props provide a medium so that components can talk to each other.  In fact, we can reduce thousands of lines of code just by using Props!     

Whenever we declare any component it can be either a class component or a functional component. One thing to notice here is, no matter what kind of component is, it should never change its props value.      

Hence the components should act like pure functions (which can’t change their own input) to their props.     

But, if you really want to change or introduce some dynamic UIs that should change within the component, you should learn about “State”.     

State allows React components to change their values over time without any violations. A state is usually called as an encapsulated one or having a local scope of the component.     

It is not accessible to any component other than the one that owns it and sets it.     

You can learn about the state in this article.     

Can we use Props and State Together?   

Absolutely  ! Let’s understand with the following example how we can combine both state and props in our component.    

import React from 'react'; 
 
class App extends React.Component { 
   constructor(props) { 
       super(props); 
       this.state = { 
           heading: "Heading from props...", 
           content: "Some Content from props..."   //Line-8 
       } 
   } 
   render() {        //Line-11 
       return ( 
           <div> 
               <Header headingProp={this.state.heading} /> 
               <Content contentProp={this.state.content} /> 
           </div> 
       ); 
   } 
} 
class Header extends React.Component { 
   render() { 
       return ( 
           <div> 
               < h1 >{this.props.headingProp}</h1> 
           </div> 
       ); 
   } 
} 
class Content extends React.Component { 
   render() { 
       return ( 
           <div> 
               < h2 >{this.props.contentProp}</h2> 
           </div> 
       ); 
   } 
} 
export default App;          

An explanation for the above snippet:  

Here we have initialized and used the state in our parent component (line number 7-8) and we have used that state by passing it down the component tree using props.   

Inside the render() (line number 11), we are setting the props data as headerProp and contentProp used in child components which are <Header> component and <Content> component.   

Now, if you change the state in the parent component, all the child components get updated, because the single source pf data is State here!    

What are the differences between props and state?  

Let’s  take a look at some high-level differences between state and props. Although they do similar things, they are used differently.   

While both are used for data manipulation, one is of private and the other is of dynamic context.      

  • Props are used to pass data from parent to child whereas the state is used for data manipulation inside the component. 
  •  We can get the value of props from the parent component, where we get the value of state object from the initial data defined in the constructor() method. 
  •  While this.props is set up by React itself, with this.state we are free to add additional fields to the component manually to store something or in a scenario that doesn’t participate in the data flow.  
  •  Props are immutable, i.e We can't change props passed to a component whereas we can change the Statei.e React uses the setState() method to update the object of a state (but within the component itself) 

Conclusion    

Props is a very crucial concept while learning React. 

In this article, you have learned about the lifeline of React, which is Props, and how we can use props in React. You have got clarity on why a component updates or re-renders when data in the props changes. 

We also saw that whenever data changes in props, the component will re-render. 

Last but not the least, let’s just recall the pointers of all of the above: 

  • Props are like parameters to a function  
  • Props cannot be changed, they are immutable  
  • A prop is a special keyword in React, that stands for properties  
  • Props can only be passed in a uni-direction i.e (parent to child)  
  • Props can be used to pass dynamic data to a component 
  • A component re-renders when data in the props change

Hope you find this article useful! 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

Join the Discussion

Your email address will not be published. Required fields are marked *

Suggested Blogs

Handling React Events - A Detailed Guide

Event handling essentially allows the user to interact with a webpage and do something specific when a certain event like a click or a hover happens. When the user interacts with the application, events are fired, for example, mouseover, key press, change event, and so on. The application must handle events and execute the code. In short, events are the actions to which javascript can respond.   The actions to which javascript can respond are called events. Handling events with react is  very similar to handling events in DOM elements. Below are some general events that you would see in and out when dealing with react based websites:  Clicking an element  Submitting a form Scrolling page Hovering an element  Loading a webpage Input field change User stroking a key Image loading Naming Events in React Handling events with react is very similar to handling events in DOM elements, although there are some syntactic differences.   React events are written in camelCase.   A function is passed as the event handler rather than string. The way to write events in html / DOM is below:        click me onclick is written in lower case in html as shown above and what action to take when this onclick event triggers is taken care of by handleClick.In React, events are named using camel case and you pass a function as event handler as shown below:  Like in a functional component, event is written like below:       click me   In class based component ,event is written like below        click me Defining Events:Events are normally used in combination with functions, and the function is not executed until the event occurs, and the combination of event, HTML element, and javascript function is called binding which means to map all three. Generic syntax is:      Example:  Create a button element and what happens when onClick event triggered is driven by the function which is func() shown below     click me Let’s see some of the event attributes:   onmouseover : The mouse is moved over an element onmouseup : The mouse button is released onmouseout : The mouse  is moved off an element onmousemove: The mouse is moved Onmousedown: mouse button is pressed  onload : A image is done loading onunload: Existing the page  onblur : Losing Focus  on element  onchange : Content of a field changes onclick: Clicking an object  ondblclick: double clicking an object  onfocus element getting a focus  Onkeydown: pushing a keyboard key Onkeyup: keyboard key is released Onkeypress: keyboard key is pressed  Onselect: text is selected These are some examples of events:                                         Events                               function testApp (){                        alert((“Hello Event”);                                                   test Clicked                  test double Clicked                     Synthetic Events When you specify an event in JSX, you are not directly dealing with regular DOM events, you are dealing with a react event type called a synthetic event.It's a simple wrapper for native event instances and every synthetic event created needs to be garbage-collected which can be resource intensive in terms of CPU. The synthetic event object has properties mentioned below:  Boolean isTrusted  DOMEvent nativeEvent number timeStamp   void preventDefault() number eventPhase Synthetic events provide an interface and reduce browser inconsistencies and the event contains required information for its propagation to work. Synthetic event is reused for performance reasons in the browser, A synthetic event is a cross-browser wrapper around the browser’s native event it has the same interface as the native event. Synthetic events are delegated to the document node. Therefore native events are triggered first and the events bubble up to document, after which the synthetic events are triggered. The synthetic event object will be reused and all the properties will be nullified after the event callback has been invoked and this is for performance reasons.The workflow of synthetic event in react is:    Element ---- > Event ---- > synthetic event  ---- > handler(e)                                |                                                      |                                |  _______  Component ________|  umber timeStamp The Basics of React Event Handling Let’s explore how to handle events in react and we will showcase the click event and how it holds good for other types of events. Let’s start with functional components by creating a  file as clickAppHandler.js.In this file let’s create a  functional component  as shown below                        Import React from ‘...react’                         function clickAppHandler() {                                function clickHandler() {                                        console.log(‘clicked’)                                         }                                  return (                                                                                  Click                                                                          )                         }                       export default clickAppHandler  When onClick event triggers clickHandler function is called as shown below and when you click the button console will print the string “clicked” After this you need the add a component in the app component. In our code above you can see on click we pass the function as event handler and you will notice that we haven't added parentheses as it becomes a function, and we do not want that and we want handler to be a function not a function call. When a new component is rendered its event handler functions are added to the mapping maintained by the react.When the event is triggered and it hits and DOM object ,react maps the event to the handler, if it matches it calls the handler. The event handling in react is declarative and the advantage of declarative way to handlers is that they are part of the User interface structure.  Let’s take a look at event handling in class components                       Import React, { Component } from ‘...react’                         class TestApp extends Component {                              clickHandler() {                                  console.log(“clicked”)                                }                                render(){                                      return(                                                                                     Click me                                                                                 )                                 }                            }                       export default TestApp You cannot return false to prevent default behaviour in React. You must call preventDefault explicitly.  In HTML it looks like below:    Click Output: It will print “Clicked”  And in React, like this:  function clickHandle(e) {       e.preventDefault();       console.log(“Handled”);   }  Click  Output : console will print “Handled”  There are some  event handlers triggered by an event in the bubbling phase which is the same as with the normal DOM API; simply attach a handler to an eventual parent of an element and any events triggered on that element will bubble to the parent as long as it's not stopped via stopPropagation along the way   Click me  Below are some of the event handlers triggered in the bubbling phase:  MouseEvents           onClick           onDrag          onDoubleClick Keyboard Events                    onKeyDown                    onKeyPress                    onKeyUp Focus Events                  onFocus   onBlur To capture an event handler for the capture phase, append capture to the event name. For example, instead of using onClick, use onClickCapture to handle the click event.  Capture event example:                  Click me    Additional ExamplesExample1                       Import React from ‘...react’                         function clickAppHandler() {                                function clickHandler() {                                        console.log(‘clicked’)                                         }                                  return (                                                                                  Click                                                                          )                         }                       export default clickAppHandler   Example2       This example is along with HTML in a single file                                                            Events                               function testApp (){                        alert((“Hello Event”);                                                   test Clicked                  test double Clicked                     Adding Events: Below example is how you add an event. Highlighted in bold                      Import React from ‘...react’                         function clickAppHandler() {                                function clickHandler() {                                        console.log(‘clicked’)                                         }                                  return (                                                                                  Click                                                                          )                         }                       export default clickAppHandler  Passing Arguments to Event HandlerThere are two ways arguments are passed to event handler  Arrow function                    this.handleClick(id,e)}>Click                onClick is the event                e is the event object                 id can be state or props or some data Bind method      Click  In this case event object is automatically passed In both methods e represents the react event and its passed after the ID as second argument,With an arrow function this event e is passed explicitly but with bind method its automatically passed.                                     Import React,{ Component } from “react”;                                         class TestApp extends Component {                                           state = {                                                       id: 2,                                                      Name: “TestApp Dummy”                                                };                                                             //arrow function                                                 handleClick = (id,e) => {                                                       console.log(id);                                                       console.log(e);                                                  };                                               handleArg = (e) => { this.handleClick(this.state.id,e);}                                                          render() {     return (                    TestApp,{this.state.name}            onClick={this.handleArg}>Display            );   }  }  The react event is an object and obtained from react. Instead of creating a separate function for passing argument, you can directly pass the anonymous arrow function as shown in the render function below:     render() {        return (                                                                                                       TestApp,{this.state.name}                                                {                           this.handleClick(this.state.id,e);                                                               }}>Display                                                                                                         );                                                 }                                            }    Output:   click on button  “TestApp Dummy “                   Let’s see only how bind method looks like in the render function    render() {                                         return (                                                                                                 TestApp,{this.state.name}                                                   Display                                                                                                       );                                                  }                                              } Output: this will display the h1 tag and when you click the button handleClick function gets invoked and the console will display id of the state object as shown above. Building a Practice to Thoroughly Understand Events This blog focuses on event handling, which in turn teaches about event handlers declared in JSX markup.This approach helps in tracking down the element mapped with events in an easy way.  We also learned how to handle multiple event handlers in a single element by using JSX attributes.we also learned about ways to bind event handler and  parameter values. Then we learned about synthetic events which are abstractions around native events. The best way you can retain this learning is by practicing more and tackling the complexities that may arise as you practice. You can find several tutorials on the internet or share your questions with us here. Happy learning! 
5355
Handling React Events - A Detailed Guide

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

MongoDB Query Document Using Find() With Example

MongoDB's find() method selects documents from a collection or view and returns a cursor to those documents. There are two parameters in this formula: query and projection.Query – This is an optional parameter that specifies the criteria for selection. In simple terms, a query is what you want to search for within a collection.Projection – This is an optional parameter that specifies what should be returned if the query criteria are satisfied. In simple terms, it is a type of decision-making that is based on a set of criteria.MongoDB's Flexible SchemaA NoSQL database, which stands for "not only SQL," is a way of storing and retrieving data that is different from relational databases' traditional table structures (RDBMS).When storing large amounts of unstructured data with changing schemas, NoSQL databases are indeed a better option than RDBMS. Horizontal scaling properties of NoSQL databases allow them to store and process large amounts of data.These are intended for storing, retrieving, and managing document-oriented data, which is frequently stored in JSON format (JavaScript Object Notation). Document databases, unlike RDBMSs, have a flexible schema that is defined by the contents of the documents.MongoDB is one of the most widely used open-source NoSQL document databases. MongoDB is known as a 'schemaless' database because it does not impose a specific structure on documents in a collection.MongoDB is compatible with a number of popular programming languages. It also offers a high level of operational flexibility because it scales well horizontally, allowing data to be spread or 'sharded' across multiple commodity servers with the ability to add more servers as needed. MongoDB can be run on a variety of platforms, including developer laptops, private clouds, and public clouds.Querying documents using find()MongoDB queries are used to retrieve or fetch data from a MongoDB database. When running a query, you can use criteria or conditions to retrieve specific data from the database.The function db.collection is provided by MongoDB. find() is a function that retrieves documents from a MongoDB database.In MongoDB, the find method is used to retrieve a specific document from the MongoDB collection. In Mongo DB, there are a total of six methods for retrieving specific records.find()findAndModify()findOne()findOneAndDelete()findOneAndReplace()findOneAndUpdate()Syntax:find(query, projection)We can fetch a specific record using the Find method, which has two parameters. If these two parameters are omitted, the find method will return all of the documents in the MongoDB collection.Example:Consider an example of employees with the database of employee_id and employee_name and we will fetch the documents using find() method.First, create a database with the name “employees” with the following code:use employeesNow, create a collection “employee” with:db.createCollection("employee")In the next step we will insert the documents in the database:db.employee.insert([{employee_id: 101, employee_name: "Ishan"}, {employee_id: 102, employee_name: "Bhavesh"}, {employee_id: 103, employee_name: "Madan"}])Find all Documents:To get all the records in a collection, we need to use the find method with an empty parameter. In other words, when we need all the records, we will not use any parameters.db.employee.find()Output in Mongo ShellThe pretty() method can be used to display the results in a formatted manner.Syntax:db.COLLECTION_NAME.find().pretty()Let’s check our documents with pretty() method:Query FiltersWe will see examples of query operations using the db.collection.find() method in mongosh.We will use the employee collection in the employees database.db.employee.insert([{employee_id: 101, employee_name: "Ishan", age: 21, email_id: "ishanjain@gmail.com"}, {employee_id: 102, employee_name: "Bhavesh", age: 22, email_id: "bhaveshg@gmail.com"}, {employee_id: 103, employee_name: "Madan", age: 23, email_id: "madan@gmail.com"}])As we have seen earlier that to select all the documents in the database we pass an empty document as the query filter parameter to the find method.db.employee.find().pretty()Find the first document in a collection:db.employee.findOne()Find a document by ID:db.employee.findOne({_id : ObjectId("61d1ae0b56b92c20b423a5a7")})Find Documents that Match Query Criteriadb.employee.find({“age”: “22”})db.employee.find({"employee_name": "Madan"}).pretty()Sort Results by a Field:db.employee.find().sort({age: 1}).pretty()order by age, in ascending orderdb.employee.find().sort({age: -1}).pretty()order by age, in descending orderAND Conditions:A compound query can specify conditions for multiple fields in the documents in a collection. A logical AND conjunction connects the clauses of a compound query indirectly, allowing the query to select all documents in the collection that meet the specified conditions.In the following example, we will consider all the documents in the employee collection where employee_id equals 101 and age equals 21.db.employee.find({"employee_id": 101, "age": "21" }).pretty()Querying nested fieldsThe embedded or nested document feature in MongoDB is a useful feature. Embedded documents, also known as nested documents, are documents that contain other documents.You can simply embed a document inside another document in MongoDB. Documents are defined in the mongo shell using curly braces (), and field-value pairs are contained within these curly braces.Using curly braces, we can now embed or set another document inside these fields, which can include field-value pairs or another sub-document.Syntax:{ field: { field1: value1, field2: value2 } }Example:We have a database “nested” and in this database we have collection “nesteddoc”.The following documents will insert into the nesteddoc collection.db.nesteddoc.insertMany([ { "_id" : 1, "dept" : "A", "item" : { "sku" : "101", "color" : "red" }, "sizes" : [ "S", "M" ] }, { "_id" : 2, "dept" : "A", "item" : { "sku" : "102", "color" : "blue" }, "sizes" : [ "M", "L" ] }, { "_id" : 3, "dept" : "B", "item" : { "sku" : "103", "color" : "blue" }, "sizes" : "S" }, { "_id" : 4, "dept" : "A", "item" : { "sku" : "104", "color" : "black" }, "sizes" : [ "S" ] } ])Place the documents in the collection now. Also, take a look at the results:As a result, the nesteddoc collection contains four documents, each of which contains nested documents. The find() method can be used to access the collection's documents.db.nesteddoc.find()Specify Equality Condition:In this example, we will select the document from the nesteddoc query where dept equals “A”.db.nesteddoc.find({dept: "A"})Querying ArraysUse the query document {: } to specify an equality condition on an array, where is the exact array to match, including the order of the elements.The following query looks for all documents where the field tags value is an array with exactly two elements, "S" and "M," in the order specified:db.nesteddoc.find( { sizes: ["S", "M"] } )Use the $all operator to find an array that contains both the elements "S" and "M," regardless of order or other elements in the array:db.nested.find( { sizes: { $all: ["S", "M"] } } )Query an Array for an Element:The following example queries for all documents where size is an array that contains the string “S” as one of its elements:db.nesteddoc.find( { sizes: "S" } )Filter conditionsTo discuss the filter conditions, we will consider a situation that elaborates this. We will start by creating a collection with the name “products” and then add the documents to it.db.products.insertMany([ { _id: 1, item: { name: "ab", code: "123" }, qty: 15, tags: [ "A", "B", "C" ] }, { _id: 2, item: { name: "cd", code: "123" }, qty: 20, tags: [ "B" ] }, { _id: 3, item: { name: "ij", code: "456" }, qty: 25, tags: [ "A", "B" ] }, { _id: 4, item: { name: "xy", code: "456" }, qty: 30, tags: [ "B", "A" ] }, { _id: 5, item: { name: "mn", code: "000" }, qty: 20, tags: [ [ "A", "B" ], "C" ] }])To check the documents, use db.products.find():$gt$gt selects documents with a field value greater than (or equal to) the specified value.db.products.find( { qty: { $gt: “20” } } )$gte:$gte finds documents in which a field's value is greater than or equal to (i.e. >=) a specified value (e.g. value.)db.products.find( { qty: { $gte: 20 } } )$lt:$lt selects documents whose field value is less than (or equal to) the specified value.db.products.find( { qty: { $lt: 25 } } )$lte:$lte selects documents in which the field's value is less than or equal to (i.e. =) the specified value.db.products.find( { qty: { $lte: 20 } } )Query an Array by Array Length:To find arrays with a specific number of elements, use the $size operator. For example, the following selects documents with two elements in the array.db.products.find( { "tags": {$size: 2} } )ProjectionIn MongoDB, projection refers to selecting only the data that is required rather than the entire document's data. If a document has five fields and you only want to show three of them, select only three of them.The find() method in MongoDB accepts a second optional parameter, which is a list of fields to retrieve, as explained in MongoDB Query Document. When you use the find() method in MongoDB, it displays all of a document's fields. To prevent this, create a list of fields with the values 1 or 0. The value 1 indicates that the field should be visible, while 0 indicates that it should be hidden.Syntax:db.COLLECTION_NAME.find({},{KEY:1})Example:We will consider the previous example of products collection. Run the below command on mongoshell to learn how projection works:db.products.find({},{"tags":1, _id:0})Keep in mind that the _id field is always displayed while executing the find() method; if you do not want this field to be displayed, set it to 0.Optimized FindingsTo retrieve a document from a MongoDB collection, use the Find method.Using the Find method, we can retrieve specific documents as well as the fields that we require. Other find methods can also be used to retrieve specific documents based on our needs.By inserting array elements into the query, we can retrieve specific elements or documents. To retrieve data for array elements from the collection in MongoDB, we can use multiple query operators.
6494
MongoDB Query Document Using Find() With Example

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

Implementing MongoDb Map Reduce using Aggregation

Algorithms and applications in today's data-driven market collect data about people, processes, systems, and organisations 24 hours a day, seven days a week, resulting in massive amounts of data. The problem is figuring out how to process this massive amount of data efficiently without sacrificing valuable insights.What is Map Reduce? The MapReduce programming model comes to the rescue here. MapReduce, which was first used by Google to analyse its search results, has grown in popularity due to its ability to split and process terabytes of data in parallel, generating results faster. A (Key,value) pair is the basic unit of information in MapReduce. Before feeding the data to the MapReduce model, all types of structured and unstructured data must be translated to this basic unit. The MapReduce model, as the name implies, consists of two distinct routines: the Map-function and the Reduce-function.  MapReduce is a framework for handling parallelizable problems across huge files using a huge number of devices (nodes), which are collectively referred to as a cluster (if all nodes are on the same local network and use similar hardware) or a grid (if the nodes are shared across geographically and administratively distributed systems, and use more heterogeneous hardware).  When data stored in a filesystem (unstructured) or a database(structured) is processed, MapReduce can take advantage of data's locality, processing it close to where it's stored to reduce communication costs. Typically, a MapReduce framework (or system) consists of three operations: Map: Each worker node applies the map function to local data and saves the result to a temporary storage. Only one copy of the redundant input data is processed by a master node. Shuffle: worker nodes redistribute data based on output keys (produced by the map function), ensuring that all data associated with a single key is stored on the same worker node. Reduce: each group of output data is now processed in parallel by worker nodes, per key. This article will walk you through the Map-Reduce model's functionality step by step. Map Reduce in MongoDB The map-reduce operation has been deprecated since MongoDB 5.0. An aggregation pipeline outperforms a map-reduce operation in terms of performance and usability. Aggregation pipeline operators like $group, $merge, and others can be used to rewrite map-reduce operations. Starting with version 4.4, MongoDB provides the $accumulator and $function aggregation operators for map-reduce operations that require custom functionality. In JavaScript, use these operators to create custom aggregation expressions. The map and reduce functions are the two main functions here. As a result, the data is independently mapped and reduced in different spaces before being combined in the function and saved to the specified new collection. This mapReduce() function was designed to work with large data sets only. You can perform aggregation operations like max and avg on data using Map Reduce, which is similar to groupBy in SQL. It works independently and in parallel on data. Implementing Map Reduce with Mongosh (MongoDB Shell)  The db.collection.mapReduce() method in mongosh is a wrapper for the mapReduce command. The examples that follow make use of the db.collection.mapReduce(). Example: Create a collection ‘orders’ with these documents: db.orders.insertMany([     { _id: 1, cust_id: "Ishan Jain", ord_date: new Date("2021-11-01"), price: 25, items: [ { sku: "oranges", qty: 5, price: 2.5 }, { sku: "apples", qty: 5, price: 2.5 } ], status: "A" },     { _id: 2, cust_id: "Ishan Jain", ord_date: new Date("2021-11-08"), price: 70, items: [ { sku: "oranges", qty: 8, price: 2.5 }, { sku: "chocolates", qty: 5, price: 10 } ], status: "A" },     { _id: 3, cust_id: "Bhavesh Galav", ord_date: new Date("2021-11-08"), price: 50, items: [ { sku: "oranges", qty: 10, price: 2.5 }, { sku: "pears", qty: 10, price: 2.5 } ], status: "A" },     { _id: 4, cust_id: "Bhavesh Galav", ord_date: new Date("2021-11-18"), price: 25, items: [ { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" },     { _id: 5, cust_id: "Bhavesh Galav", ord_date: new Date("2021-11-19"), price: 50, items: [ { sku: "chocolates", qty: 5, price: 10 } ], status: "A"},     { _id: 6, cust_id: "Madan Parmar", ord_date: new Date("2021-11-19"), price: 35, items: [ { sku: "carrots", qty: 10, price: 1.0 }, { sku: "apples", qty: 10, price: 2.5 } ], status: "A" },     { _id: 7, cust_id: "Madan Parmar", ord_date: new Date("2021-11-20"), price: 25, items: [ { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" },     { _id: 8, cust_id: "Abhresh", ord_date: new Date("2021-11-20"), price: 75, items: [ { sku: "chocolates", qty: 5, price: 10 }, { sku: "apples", qty: 10, price: 2.5 } ], status: "A" },     { _id: 9, cust_id: "Abhresh", ord_date: new Date("2021-11-20"), price: 55, items: [ { sku: "carrots", qty: 5, price: 1.0 }, { sku: "apples", qty: 10, price: 2.5 }, { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" },     { _id: 10, cust_id: "Abhresh", ord_date: new Date("2021-11-23"), price: 25, items: [ { sku: "oranges", qty: 10, price: 2.5 } ], status: "A" }  ]) Apply a map-reduce operation to the orders collection to group them by cust_id, then add the prices for each cust_id: To process each input document, define the map function: this refers the document that the map-reduce operation is processing in the function. For each document, the function maps the price to the cust_id and outputs the cust_id and price. var mapFunction1 = function() {emit(this.cust_id, this.price);}; With the two arguments keyCustId and valuesPrices, define the corresponding reduce function: The elements of the valuesPrices array are the price values emitted by the map function, grouped by keyCustId. The valuesPrice array is reduced to the sum of its elements by this function. var reduceFunction1 = function(keyCustId, valuesPrices) {return Array.sum(valuesPrices);};Apply the mapFunction1 map function and the reduceFunction1 reduce function to all documents in the orders collection: db.orders.mapReduce(mapFunction1,reduceFunction1,{ out: "map_reduce_example" }) The results of this operation are saved in the map_reduce_example collection. If the map_reduce_example collection already exists, the operation will overwrite its contents with the map-reduce operation's results. Check the map_reduce_example collection to verify: db.map_reduce_example.find().sort( { _id: 1 } ) Aggregation Alternative:You can rewrite the map-reduce operation without defining custom functions by using the available aggregation pipeline operators: db.orders.aggregate([{$group: { _id:"$cust_id",value:{$sum: "$price" } } },{ $out: "agg_alternative_1" }]) Check the agg_alternative_1 collection to verify: db.agg_alternative_1.find().sort( { _id: 1 } )Implementing Map Reduce with Java Consider the collection car and insert the following documents in it. db.car.insert( [ {car_id:"c1",name:"Audi",color:"Black",cno:"H110",mfdcountry:"Germany",speed:72,price:11.25}, {car_id:"c2",name:"Polo",color:"White",cno:"H111",mfdcountry:"Japan",speed:65,price:8.5}, {car_id:"c3",name:"Alto",color:"Silver",cno:"H112",mfdcountry:"India",speed:53,price:4.5}, {car_id:"c4",name:"Santro",color:"Grey",cno:"H113",mfdcountry:"Sweden",speed:89,price:3.5} , {car_id:"c5",name:"Zen",color:"Blue",cno:"H114",mfdcountry:"Denmark",speed:94,price:6.5} ] ) You will get an output like this:  Let's now write the map reduce function on a collection of cars, grouping them by speed and classifying them as overspeed cars.  var speedmap = function (){  var criteria;  if ( this.speed > 70 ) {criteria = 'overspeed';emit(criteria,this.speed);}}; Based on the speed, this function classifies the vehicle as an overspeed vehicle. The term "this" refers to the current document that requires map reduction. var avgspeed_reducemap = function(key, speed) {       var total =0;       for (var i = 0; i 
7344
Implementing MongoDb Map Reduce using Aggregation

Algorithms and applications in today's data-driven... Read More