React Components Lifecycle | React Tutorial for Beginners | ReactJS Training | Edureka

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Agenda
 What Is Artificial Intelligence ?
 What Is Machine Learning ?
 Limitations Of Machine Learning
 Deep Learning To The Rescue
 What Is Deep Learning ?
 Deep Learning Applications

Agenda
React
Components1
State
Props
Life Cycle Of
Components5
Flow Of Stateless
& Stateful
Components
4
1 3
4
2
5

React Components

React Components
1
3
4
2
5
In React everything is a component
Browser

React Components
1
3
4
2
5
All these components are integrated together to build one application
Browser

React Components
1
3
4
2
5
We can easily update or change any of these components without disturbing the rest of the application
Browser

React Components – UI Tree
Single view of UI is divided into logical pieces. The starting component becomes the root and rest components
become branches and sub-branches.
1
3
4
2
5
Browser
1
4
32
UITree
5

ReactJS Components – Sample Code
Each component returns ONE DOM element, thus JSX elements must be wrapped in an enclosing tag
Hello World
Welcome To Edureka
3
4
2
5
class Component1 extends React.Component{
render() {
return(
<div>
<h2>Hello World</h2>
<h1>Welcome To Edureka</h1>
</div>
);
}
}
ReactDOM.render(
<Component1/>,document.getElementById('content')
);
Enclosing Tag

Prop State
React Components
React components are controlled either by Props or States

Props

{this.props.name}
Props
{this.props.name}
Props help components converse with one another.
class Body extends
React.Component({
render (){
return(
<Header name =“BOB”/>
<Footer name =“ALEX”/>
);
}
});
<Body/>
<Header/>
<Footer/>
BOB
ALEX

{this.props.name}
Props
{this.props.name}
Using Props we can configure the components as well
class Body extends
React.Component({
render (){
return(
<Header name =“MILLER”/>
<Footer name =“CODDY”/>
);
}
});
<Body/>
<Header/>
<Footer/>
MILLER
CODDY

Props
Props Props
Props Props
Props
Components
Components
Components
Components
Components
Data flows downwards from the parent component
Uni-directional data flow
Props are immutable i.e pure
Can set default props
Work similar to HTML attributes1
2
3
4
5

Props
var Body = React.createClass(
{
render: function(){
return (
<div>
<h1 > Hello World from Edureka!!</h1>
<Header name = "Bob"/>
<Header name = "Max"/>
<Footer name = "Allen"/>
</div>
);
}
}
);
Parent Component
Sending Props
ES5

Props
var Header = React.createClass({
render: function () {
return(
<h2>Head Name: {this.props.name} </h2>
);
}
});
var Footer = React.createClass({
render: function () {
return(
<h2>Footer Name: {this.props.name}</h2>
);
}
});
ReactDOM.render(
<Body/>, document.getElementById('container')
);
Child Components
Receiving Props
ES5

State

State
Components can change, so to keep track of updates over the time we use state
Increase In
Temperature
ICE WATER
State changes because of some event

State
Unlike Props, component States are mutable1
Core of React Components3
Objects which control components rendering and behavior
Must be kept simple
2
4
Props Props
Props Props
Props
Components
Components
Components
Components
Components
State
State
State
State

State
Compone
nt
Compone
nt
Compone
nt
Component
StatefulStateless
Dumb Components Smart Components

State
STATEFUL
<Component/>
STATELESS
<Component/>
STATELESS
<Component/>
• Calculates states internal state of components
• Contains no knowledge of past, current and possible future
state changes
Stateless
• Core which stores information about components state in
memory
• Contains knowledge of past, current and possible future state
changes
Stateful

Flow Of Stateless & Stateful
Components

class MyApp extends React.Component {
constructor(props) {
super(props);
this.state = { isLoggedIn: false }
}
receiveClick() {
this.setState({ isLoggedIn: !this.state.isLoggedIn });
}
Flow Of Stateless & Stateful Components
Parent Component
Setting Initial State
Changing State
ES6

render() {
return(
<div>
<h1>Hello.. I am Stateful Parent Component</h1><br/>
<p>I monitor if my user is logged in or not!!</p> <br/>
<p>Let's see what is your status : <h2><i>{this.state.isLoggedIn ?
'You Are Logged In' : 'Not Logged In'}</i></h2></p><br/>
<h2>Hi, I am Stateless Child Component</h2>
<p>I am a Logging Button</p><br/>
<p><b>I don't maintain state but I tell parent component if user clicks me
</b></p><br/>
<MyButton click={this.receiveClick.bind(this)} isLoggedIn= {this.state.isLoggedIn}/>
</div>
);
}
}
Passing Props To Child
Component
ES6

State Changes

Component Lifecycle

Lifecycle Phases
Lifecycle methods notifies when certain stage of
the lifecycle occurs
Code can be added to them to perform various
tasks
Provides a better control over each phase
04
01
02
03

Lifecycle Phases
1
In this phase,
component is
about to make its
way to the DOM04
01
02
03

Lifecycle Phases
In this phase,
component can
update & re-render
when a state change
occurs
204
01
02
03

Lifecycle Phases
In this phase,
component can
update & re-render
when a prop change
occurs
304
01
02
03

Lifecycle Phases
In this phase, the
component is
destroyed and
removed from DOM 404
01
02
03

Component Lifecycle In A Glance
componentWillUnmount()
shouldComponentUpdate(nextProps,nextState)
componentWillUpdate(nextProps,nextState)
componentsWillReceiveProps(nextProps)
componentDidUpdate(prevProps, prevState)
render()
can use this.state
getInitialState()
componentWillMount()
getDefaultProps()
componentDidMount()
render()
ReactDOM.render()
ReactDOM.unmount
ComponentAtNode()
setProps()
setStates()
forceUpdate()
true
false

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