Introduction to React

Rosy Shrestha

 

https://github.com/shrestharosy/introduction-to-react​

React Library

Why React?

  1. Declarative
  2. Component-based
  3. Suitable for web and mobile
  4. Small learning curve

Why React?

  1. Declarative
  • you describe the picture and someone else implements it
  • we change the state and the UI is updated
  • no direct DOM interactions
  • web applications runs much faster (VDOM)

Why React?

2. Component Based

  • each component  has its own markup and logic
  • reusability, hence DRY (Don't Repeat Yourself)
  • less development time

Why React?

2. Component Based

Why React?

3. Suitable for both web and mobile apps

  • React Native derived from  React for mobile applications

Why React?

4. Small learning curve

  • Combines concept of HTML and JavaScript with some benefits

Before we start

Install node (Node >= 10.16 and npm >= 5.6)

https://nodejs.org/en/download/package-manager/

 

Install yarn

https://classic.yarnpkg.com/en/docs/install

 

 

npm install --global yarn

Create React App

npm install -g create-react-app

yarn create-react-app introduction-to-react



npx create-react-app introduction-to-react

Recommended

JSX

(JavaScript Syntax Extension)

JSX

  • JavaScript + XML

 

 

const name = "Rosy"
const course = "React"

const element = 
<div className="introduction">
	Ola! I am {name} and I am learning {course} for {5*4} minutes
</div>

JSX

  • JavaScript + XML

 

 

const name = "Rosy"
const course = "React"

const element = 
<div className="introduction">
	Ola! I am {name} and I am learning {course} for {5*4} minutes
</div>

must return a single element (alternatively use, <React.Fragment> </React.Fragment> or <> </>)

<>
	<h1>blah</h1>
    <span>what</span>
    <p>ola</p>
</>

JSX

  • JavaScript + XML

 

 

const name = "Rosy"
const course = "React"

const element = 
<div className="introduction">
	Ola! I am {name} and I am learning {course} for {5*4} minutes
</div>

use className instead of class
camelCase attributes (onClick, onSubmit)
use curly branches for expressions

React Element

const name = "Rosy";
const course = "React";

const element =
      /*#__PURE__*/
React.createElement(
"div", 
{
  className: "introduction"
}, 
"Ola! I am ", name, " and I am learning ", course, " for ", 5 * 4, " minutes"
);

//Syntax
React.createElement(component, props, ...children)

React Element

const element = {
  type: 'div',
  props: {
    className: 'introduction',
    children: "Ola! I am ", name, " and I am learning ", course, " for ", 5 * 4, " minutes"
  }
};

Render

const name = "Rosy"
const course = "React"

const element = 
<div className="introduction">
	Ola! I am {name} and I am learning {course} for {5*4} minutes
</div>


//syntax
ReactDOM.render(componentToRender, targetNode)

DOM (Document Object Model)

DOM (Document Object Model)

JSX render and Virtual DOM

  • VDOM is a simplified copy of the real DOM
  • React Element can be inserted into the VDOM, compared and updated fast and easily

State changes

Creates a VDOM with new update

Compares with previous VDOM state

Change in  state

Updates only those changes in DOM

https://reactjs.org/docs/rendering-elements.html

  • ES6+
  • Each child in a list should have a unique "key" prop warning. Why?
  • Explore array methods
  • Difference between regular and arrow functions
  • Create your own stateful and stateless components

Look Into...

Look Into...

https://gist.github.com/shrestharosy028/acefce7629763f4dc9a65d03e78802ba#file-moodswing-jsx

React Lifecycle Phases

  1. Mounting
  2. Updating
  3. Unmounting

https://projects.wojtekmaj.pl/react-lifecycle-methods-diagram/

React Lifecycle Phases

Mounting
when component renders for the first time 

  • constructor ( )
  • render ( )
  • componentDidMount ( )

React Lifecycle Phases

  • constructor ( )
    • initialize local state
    • bind event handler to an instance

Mounting

React Lifecycle Phases

  • render ( )
    • returns single root HTML node element
    • handles rendering of component to UI

Mounting

React Lifecycle Phases

  • componentDidMount ( )
    • called immediately after component is rendered
    • API calls, subscriptions

Mounting

React Lifecycle Phases

Updating
update existing nodes in the DOM 

  • render ( )
  • componentDidUpdate ( )

React Lifecycle Phases

Updating

  • componentDidUpdate ( )
    • called after componentDIdMount()
    • takes previous props and previous state as arguments

React Lifecycle Phases

Updating

  • componentDidUpdate ( prevProps, prevState)
componentDidUpdate(prevProps, prevState) {
 const currentProps = this.props
 if (currentProps.name !== prevProps.name) {
//    do something
 }
}

React Lifecycle Phases

Unmounting

  • componentWillUnmount ( )
    • invoked immediately before a component is unmounted and destroyed
    • perform cleanups, cancel network requests

React Lifecycle Phases

Unmounting

  • componentWillUnmount ( )
    • DON'T call setState() in this method 

React Routers

  • allows user to move between your components and different URLs
  • Install react-router-dom for routing
npm i react-router-dom

yarn add react-router-dom

React Routers

function Routes(){
 return (
  <BrowserRouter>
    <Switch>
   	 <Route path={'/main'} component={Main}>
  	 <Route path={'/profile'} component={Profile}>
    </Switch>
  </BrowserRouter>
) 
}

Look into:

Introduction to React

By Rosy Shrestha

Source: Aishwarya Shrestha

Introduction to React

  • 105