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How to avoid binding by using arrow functions in callbacks in ReactJS?
  • Last Updated : 30 Sep, 2020

In React class-based components when we use event handler callbacks, it is very important to give special attention to the ‘this’ keyword. In these cases the context this is undefined when the callback function actually gets invoked that’s why we have to bind the context of this. Now if binding all the methods of each class is very annoying. Instead of binding we can use the inline arrow function since the arrow function does not have its own value of this, it uses the parent or public value. Using the inline arrow function we can get rid of annoying method binding every time and also the code looks very packed and organized.

Example 1: This example illustrates how to use arrow functions in callbacks

  • index.js:

    Javascript

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    import React from 'react'
    import ReactDOM from 'react-dom'
    import App from './App'
      
    ReactDOM.render(<App />, document.querySelector('#root'))

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  • App.js : 



    Javascript

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    import React, { Component } from 'react'
      
    class App extends Component {
      // Default props
      static defaultProps = {
        courceContent : [
          'JSX', 'React Props', 'React State', 'React Lifecycle Methods',
          'React Event Handlers', 'React Router', 'React Hooks', 'Readux',
          'React Context'
        ]
      }
        
      constructor(props){
        super(props)
          
        // Set initial state
        this.state = {msg : 'React Cource', content:''}
      }
      
      // Return an unordered list of contents
      renderContent(){
        return (
          <ul>
            {/* map over all the contents and
                return some JSX for each  */}
            {this.props.courceContent.map(content => (
              <li>{content}</li>
            ))}
          </ul>
        
      }
        
      render(){
        const button = !this.state.content && 
        <button 
          // Arrow function in callback
          onClick={() => {
            // Update state
            this.setState({
              msg : 'Cource Content',
              content : this.renderContent()
            })
          }}
        >
          Click here to know contents!
        </button>
        return (
          <div>
              
    <p>{this.state.msg}</p>
      
              
    <p>{this.state.content}</p>
      
            {button}
          </div>
        )
      }
    }
      
    export default App

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Output :

Example 2 :

  • index.js : 

    Javascript

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    import React from 'react'
    import ReactDOM from 'react-dom'
    import App from './App'
      
    ReactDOM.render(<App />, document.querySelector('#root'))

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  • App.js : 

    Javascript

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    import React, { Component } from 'react'
      
    class App extends Component{
      // Default props 
      static defaultProps = { 
        name : ['John', 'Alex', 'Bob'
      
      constructor(props){ 
        super(props) 
        // Nnitialize count state 
        this.state = {msg : 'Hi There', count:0}
      
      
      render(){ 
        return
          <div> 
            <h3>Greetings!</h3>     
              
    <p>{this.state.msg}</p>
      
            <button 
              // Arrow function in callback
              // does not required explicit binding
              onClick={() => {
                this.setState(st => (
                  st.msg = `${st.msg}, ${this.props.name[st.count]}`,
                  st.count += 1
                ))
              }}
            
              Say greeting to employees! 
            </button> 
          </div>    
        )  
      
    }
    export default App

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Output :

react-js-img




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