React Component API

ReactJS component is a top-level API. It makes the code completely individual and reusable in the application. It includes various methods for:

Creating elements
Transforming elements
Fragments

Here, we are going to explain the three most important methods available in the React component API.

setState()
forceUpdate()
findDOMNode()

setState()

This method is used to update the state of the component. This method does not always replace the state immediately. Instead, it only adds changes to the original state. It is a primary method that is used to update the user interface(UI) in response to event handlers and server responses.

Note: In the ES6 classes, this.method.bind(this) is used to manually bind the setState() method.

Syntax

In the above syntax, there is an optional callback function which is executed once setState() is completed and the component is re-rendered.

Example

  import React, { Component } from ‘react’;  import PropTypes from ‘prop-types’;  class App extends React.Component {     constructor() {        super();        this.state = {            msg: “Welcome to Tutor Aspire”        };        this.updateSetState = this.updateSetState.bind(this);     }     updateSetState() {         this.setState({            msg:”Its a best ReactJS tutorial”         });     }     render() {        return (           <div>               <h1>{this.state.msg}</h1>               <button onClick = {this.updateSetState}>SET STATE</button>           </div>        );     }  }  export default App;  

Main.js

  import React from ‘react’;  import ReactDOM from ‘react-dom’;  import App from ‘./App.js’;    ReactDOM.render(<App/>, document.getElementById(‘app’));  

Output:

React Component API

When you click on the SET STATE button, you will see the following screen with the updated message.

React Component API

forceUpdate()

This method allows us to update the component manually.

Syntax

Example

App.js

  import React, { Component } from ‘react’;  class App extends React.Component {     constructor() {        super();        this.forceUpdateState = this.forceUpdateState.bind(this);     }     forceUpdateState() {        this.forceUpdate();     };     render() {        return (           <div>               <h1>Example to generate random number</h1>               <h3>Random number: {Math.random()}</h3>               <button onClick = {this.forceUpdateState}>ForceUpdate</button>           </div>        );     }  }  export default App;  

Output:

React Component API

Each time when you click on ForceUpdate button, it will generate the random number. It can be shown in the below image.

React Component API

findDOMNode()

For DOM manipulation, you need to use ReactDOM.findDOMNode() method. This method allows us to find or access the underlying DOM node.

Syntax

Example

For DOM manipulation, first, you need to import this line: import ReactDOM from ‘react-dom‘ in your App.js file.

App.js

  import React, { Component } from ‘react’;  import ReactDOM from ‘react-dom’;  class App extends React.Component {     constructor() {        super();        this.findDomNodeHandler1 = this.findDomNodeHandler1.bind(this);        this.findDomNodeHandler2 = this.findDomNodeHandler2.bind(this);     };     findDomNodeHandler1() {         var myDiv = document.getElementById(‘myDivOne’);         ReactDOM.findDOMNode(myDivOne).style.color = ‘red’;     }     findDomNodeHandler2() {         var myDiv = document.getElementById(‘myDivTwo’);         ReactDOM.findDOMNode(myDivTwo).style.color = ‘blue’;     }     render() {        return (           <div>               <h1>ReactJS Find DOM Node Example</h1>               <button onClick = {this.findDomNodeHandler1}>FIND_DOM_NODE1</button>               <button onClick = {this.findDomNodeHandler2}>FIND_DOM_NODE2</button>               <h3 id = “myDivOne”>JTP-NODE1</h3>               <h3 id = “myDivTwo”>JTP-NODE2</h3>           </div>        );     }  }  export default App;  

Output:

React Component API

Once you click on the button, the color of the node gets changed. It can be shown in the below screen.

React Component API

Next TopicReact Component Life-Cycle

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React Component API

React Component API

setState()

Note: In the ES6 classes, this.method.bind(this) is used to manually bind the setState() method.

Syntax

Example

forceUpdate()

Syntax

Example

findDOMNode()

Syntax

Example

T-Test in R

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