FrontEnd/React_Intro.txt at main · shortnotes/FrontEnd · GitHub

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We require mainly 2 appl softwares.

1. node.js installation
2. visual studio code


react or react.js or react.jsx


How to create a project in ReactJs:
----------------------------------------
here we follows the given steps

step1: we create a one folder in any other drive name
        D:\>test_reactjs
step2: open vscode from file menu select open folder option
step3: select our folder name in the existing  path
step4: from the menu select terminal option
step5:from the terminal path create reactjs project in the following way
      npx create-react-app projectname


	  Ex: npx create-react-app react_demo
OR

      -->npm cache clean --force
	  -->npm install npm@latest -g
	  -->npm install
	  -->npx create-react-app react_demo

OR    -->npm install -g create-react-app
         npx create-react-app react_demo


step6: enter into our reactjs project we type as follows
       d:>test_react>
	   d:>test_react>cd react_demo
	   d:>test_reat>react_demo>-

step7:  we will start the project
        npm start


How in react it display content on Browser:
		----------------------------------------
	By default the data flow from

	     app.js file -->index.js -->index.html

		     OR
 index.js->index.html

 Introduction:
 ----------------
 react or reactjs or react.js
 it is an open source front end application depends on javscript
 library.

 Developed by Facebook organization,
 " Jordan walke " in the year 2013.


 reactjs     Angular   vue


 using reactjs application we develop user interface concepts on a webpage.

 React is not a framework ,  Angular we say that it is a framework,
 React js open source application,
 react js application useful for to develop user interface concepts


 Features of React Js application:
 -----------------------------------------

 ->it follows jsx concept (javascript xml synatx)
 ->react js application we called as component based application
    (Single page application)
	here we reused same components in the application
 -> Uni directional based application (One directional flow of data)


		 jsx (javascript xml)
		 --------------------------------
jsx stands for javscript xml.
jsx allows us to write HTML in React
jsx makes it easier to write and edit HTML in React.


Babel Compiler:
-----------------------------
In Reactjs here babel is called as javascript compiler .
it converts javscript library code into html code.

here babel it converst JSX code into normal html code.


JSX code:
==========================================

index.js
---------------------------------------------------------------------
	  import React from 'react';
import ReactDOM from 'react-dom';


ReactDOM.render( <h1>Hello World</h1>,  document.getElementById('root'));


index.html
-----------------------------------
<!DOCTYPE html>
<html lang="en">
  <head>

  </head>
  <body>

    <div id="root"></div>

  </body>
</html>


div tag in jsx:
-----------------------------------------------------------------------
in ReactDOM  whenever we add multiple elements or tags
then we should include <div> tag.


import React from 'react';
import ReactDOM from 'react-dom';


ReactDOM.render( <div><h1>Hello World</h1> <p>welcome to react</p></div>,  document.getElementById('root'));


Expressions inJSX:
-------------------------------------
we need to add expression jsx then we should include
inside of the curly brackets.

{}


import React from 'react'
import ReactDOM from 'react-dom'


ReactDOM.render( <h2>shravan {2+4}</h2>,  document.getElementById('root'));


Ex2:
----------------------

import React from 'react'
import ReactDOM from 'react-dom'


const name='corporate Trainer'
ReactDOM.render( <h2>shravan {name}</h2>,  document.getElementById('root'));


-----------------------------
Ex3:
import React from 'react'
import ReactDOM from 'react-dom'


const name=(
<ul>
<ol>Apples</ol>
<ol>Mangos</ol>
<ol>Cherris</ol>
</ul>

)
ReactDOM.render( <h2>{name}</h2>,  document.getElementById('root'));


Ex4:
------------------------------------
import React from 'react'
import ReactDOM from 'react-dom'


const name=(
<table border="1">
<thead>
<th>Employee Name</th>
<th>Employee Designation</th>
</thead>
<tbody>
<tr>
<td>Shravan Kumar</td>
<td>Corporate Trainer</td>
</tr>
<tr>
<td>Kumar</td>
<td>developer</td>
</tr>
</tbody>
</table>
)
ReactDOM.render( <h2>{name}</h2>,  document.getElementById('root'));


components in React Js:
-----------------------------
component is one of the part or position on web page.
in react js to create a component then user follows in
2 ways.

1. fucntional components
2. class components


1. fucntion components:
-----------------------------------------

App.js
-------------------

import React from 'react'
import Test from './components/Test'
import Test1 from './components/Test1'

export default function App()
{
  return(
    <div>
<h2>welcome to functional component</h2>
<Test></Test>
<Test1></Test1>
</div>
  )
}


in this example i create one folder under src
i.e components

inside of this components folder we creted two child functional components.


Test1.js
----------------
import React from 'react'
function Test1()
{
    return(
        <h2>child 1 component</h2>
    )
}
export default Test1


Test.js
----------
import React from 'react'
function Test()
{
    return(
        <h2>this is child component</h2>
    )
}
export default Test


index.js
-------------------------------
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import reportWebVitals from './reportWebVitals';

ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  document.getElementById('root')
);


reportWebVitals();


Example2:
-----------------------
App.js
--------
import React from 'react'
import Table from './components/Table'


function App()
{
  return (
<div>
<h1>This is Root component in React</h1>
<Table></Table>
</div>
  )
}
export default App


Table.js
---------------------------
import TableHeader from './TableHeader'
import TableBody from './TableBody'
import React from 'react'

export default function Table()
{
    return(
        <div>
        <table border="2">
        <TableHeader></TableHeader>
        <TableBody></TableBody>
        </table>
        </div>
    )
}


TableHeader.js
------------------
import React from 'react'
export default function TableHeader()
{
    return (
        <thead>
        <th>Employee Name</th>
        <th>Employee Designation</th>
        </thead>
    )
}


TableBody.js
---------------------
import React from 'react'
export default function TableBody()
{
    return(
        <tbody>
        <tr>
        <td>Shravan</td>
        <td>Trainer</td>
        </tr>
        </tbody>
    )
}


Arrow function in React:
--------------------------------
import TableHeader from './TableHeader'
import TableBody from './TableBody'
import React from 'react'

const Table=()=>
{
    return(
        <div>
        <table border="2">
        <TableHeader></TableHeader>
        <TableBody></TableBody>
        </table>
        </div>
    )
}
export default Table


2. Class Component:
--------------------------------------
syntax:


import React ,{ Component} from 'react';

class classname extends Component{
render()
{
return(
jsx code
)

}

}
export default classname;


App.js
---------------
import React from 'react'
import Table from './components/Table'


function App()
{
  return (
<div>
<h1>This is Root component in React</h1>
<Table></Table>
</div>
  )
}
export default App


Table.js
-----------------
import React,{Component} from 'react'
import TableHeader from './TableHeader'
import TableBody from './TableBody'

class Table extends Component{
    render()
    {
        return(
            <table border="2">
            <TableHeader></TableHeader>
            <TableBody></TableBody>
            </table>
        )
    }
}
export default Table


TableBody.js
-----------------------------------------------
import React, {Component} from 'react'

export default class TableBody extends Component
{
    render()
    {
        return (
            <tbody>
            <tr>
            <td>Shravan</td>
            <td>Corporate Traier</td>
            </tr>
            </tbody>
        )
    }
}


TableHeader.js
----------------------------------------------------
import React, { Component } from 'react'

export default class TableHeader extends Component{
    render()
    {
        return(
            <thead>
            <th>Employee Name</th>
            <th>Employee Designation</th>
            </thead>
        )
    }
}


Props:
properties

The props works as for sending or pass the data from one component into another component.
we declare in reactjs as props

React here the data flow between from one component to another only
based on uni directional

Once we pass the  data from one component into another component then
after we cannot change the data .


 Example program on functional components with props
App.js
-------------------------------------
import React from 'react'
import Test from './Test'

function App ()
{

        return(
            <div>
<Test name="shravan reddy"  desig="Corporate Trainer"></Test>
<Test name="Ajay reddy"  desig="Corporate Trainer"></Test>
<Test name="Surender reddy"  desig="Corporate Trainer"></Test>
</div>
        )

}
export default App


Test.js
--------------------------------------
import React from 'react'

const Test=(props)=>
{
    return(
        <div>
        <h1>Hello How r u  {props.name} works as {props.desig}</h1>
        </div>

    )
}
export default Test


	Example program on Class component with props:
	====================================================


	App.js
	-----------------------------------
import React, { Component } from 'react'
import Test from './Test'

class App extends Component
{
    render()
    {
                return(
            <div>
<Test name="shravan reddy"  desig="Developer"></Test>
<Test name="Ajay reddy"  desig="Trainer"></Test>
<Test name="Surender reddy"  desig="Tester"></Test>
</div>
        )
                }

}
export default App


Test.js:
---------------------------------------------

import React, {Component} from 'react'

class Test extends Component
{
    render()
    {
        return(
<h2>Name is {this.props.name} Designation is: {this.props.desig}</h2>

        )
    }

}
export default Test


React State and setState():
--------------------------------------------
The state is a builtin object in React component.
in the state object we store property values that belong to the component.

when the state object changes , the component also renders.


In react if we define state object then we follows the given syantx:


class classname extends Component{
constructor(props)
{
supper(props)
this.state={
-------
---------------
-----------------
}
}
}


index.js:
--------------------------------------------------------------

import React from 'react'
import ReactDOM from 'react-dom'
import StudentComponent from './StudentComponent'


ReactDOM.render( <StudentComponent/>,  document.getElementById('root'));


StudentComponent.js
---------------------------------------------

import React, {Component} from 'react'

class StudentComponent extends Component
{

constructor(props)
{
super(props)
this.state=
{
    firstName:"reddy",
    lastName:"shravan",
    rollNo:101,
    age: 25
}

}


render()
{
    return(
<div>
<h1>First name: {this.state.firstName}</h1>
<h1>last name: {this.state.lastName}</h1>
<h1>Roll No is: {this.state.rollNo}</h1>
<h1>Age is: {this.state.age}</h1>
</div>

    )
}

}
export default StudentComponent


	*****setState() method :

	If user wants to change the state object properties values in run time
	then user follows done of the hook i.e setState() method includes in
	application.


	In the below example program using event trigger Mechanism we invoked
	setState() method in React.


	StudentComponent.js
	========================
	import React, {Component} from 'react'

class StudentComponent extends Component
{

constructor(props)
{
super(props)
this.state=
{
    firstName:"kumar",
    lastName:"shravan",
    rollNo:101,
    age: 25
}
}
updateStudent(){
    this.setState(
        {
            rollNo: 102,
            age: 30
        }
    )
}

render()
{
    return(
<div>
<h1>First name: {this.state.firstName}</h1>
<h1>last name: {this.state.lastName}</h1>
<h1>Roll No is: {this.state.rollNo}</h1>
<h1>Age is: {this.state.age}</h1>
<button type="button" onClick={()=>this.updateStudent()}>update student</button>
</div>

    )
}

}
export default StudentComponent


Note:


The difference between state object and Props is

-------------------------------------------------------

1. using props we pass the data from one component into another component
  using state object we pass the data within the component.
2. in props mechanism we cannopt possible to change the properties values
   In state object mechanism it possible to change the properties values.

3. In props there no hook method implementation
  in state object using setState() we change the properties values at run time


  Handling Events in React:
  ---------------------------------------------------------

  Handling Events with react elements is very similer to handling
events on DOM elemets.

There are few differences between the events.


In React application events are named using camelCase styles.


How we apply the event in React application  is:

<button onClick={button is clicked} >
clcik the button
</button>


if u take example in javascript how we apply the event is

<button onClick="display()">
click  here
</button>


Handling onClick event in the class component example:
--------------------------------------------------------
In the below example represents Event Trigger Mechanism in react
application. in this example we create one of the event i.e onClick()


index.js
------------------------------------
import React from 'react'
import ReactDOM from 'react-dom'
import ClassClick from './ClassClick'


ReactDOM.render( <ClassClick/>,  document.getElementById('root'));


ClassClick.js
--------------------------------------------------------

import React, {Component} from 'react'

class ClassClick extends Component{

    clickHandler()
    {
console.log('onclick event triggered')
    }
render()
{
    return(
<div>
<button onClick={this.clickHandler}>click here</button>
</div>

    )
}

}
export default ClassClick


Example2:  using App.js file
---------------

index.js
---------------------------------------------------
import React from 'react'
import ReactDOM from 'react-dom'
import App from './App'


ReactDOM.render( <App/>,  document.getElementById('root'));


ClassClick.js
-------------------------------------------------------------

import React, {Component} from 'react'

class ClassClick extends Component{

    clickHandler()
    {
console.log('onclick event triggered')
    }
render()
{
    return(
<div>
<button onClick={this.clickHandler}>click here</button>
</div>

    )
}

}
export default ClassClick


App.js
---------------------------
import React,{ Component} from 'react'
import ClassClick from './ClassClick'

class App extends Component{
    render()
    {
        return(
            <div>
            <ClassClick></ClassClick>
            </div>
        )
    }
}
export default App


handling onclick event inthe functional component:
===================================================================

index.js-
--------
import React from 'react'
import ReactDOM from 'react-dom'
import FunctionClick from './FunctionClick';


ReactDOM.render( <FunctionClick/>,  document.getElementById('root'));


FunctionaClick.js
---------------------------------------------------------------
import React from 'react'
function FunctionClick()
{
    function clickHandler()
    {
        console.log("Functional component event")
    }

return(
    <div>
    <button onClick={clickHandler}>click here</button>
    </div>
)
}
export default FunctionClick


Binding Event in React:
--------------------------------------------
In react Applicaion in eventhandling if we declare the keyword as this
then it return the current object only.

but if we declare again this keyword in the method definition then we get Error
because the reason is this keyword exist in multiple location.

So over come this we implement bind() method in event handling mechanism.
'


EventBind.js
---------------------------------------------------------------------
import React,{Component} from 'react'

class EventBind extends Component{
    constructor(){
        super()
        this.state={
            message: "Hello"
        }
    }
    clickHandler()
    {
        console.log(this)
        this.setState({message: "good bye"})
    }
    render()
    {
        return(
<div>
<button onClick={this.clickHandler}>Click here</button>