Use onChange Event in React Functional Components

Create ReactJS Project

Create new folder named LearnReactJSWithRealApps and select to this folder in Visual Studio Code

Open Terminal windows in Visual Studio Code and use commands below:

npm install create-react-app@latest
npx create-react-app myapp

Create New Component

Open App.js file in src folder and create new component as below:

import React, { useState } from 'react';

function App() {

  let [result1, setResult1] = useState('');
  let [result2, setResult2] = useState('');
  let [result3, setResult3] = useState('');
  let [result4, setResult4] = useState('');

  let hello = (e) => {
    setResult1('Hello ' + e.target.value);
  }

  let selectCategory = (e) => {
    setResult2(e.target.value + ' is selected');
  }

  let selectFile = (e) => {
    var selectedFile = e.target.files[0];
    let result = 'File name: ' + selectedFile.name;
    result += '<br>File type: ' + selectedFile.type;
    result += '<br>File size: ' + selectedFile.size;
    setResult3(result);
  }

  let selectFiles = (e) => {
    let selectedFiles = e.target.files;
    let result = '';
    for (var i = 0; i < selectedFiles.length; i++) {
      result += '<br>File name: ' + selectedFiles[i].name;
      result += '<br>File type: ' + selectedFiles[i].type;
      result += '<br>File size: ' + selectedFiles[i].size;
      result += '<br>--------------------------';
    }
    setResult4(result);
  }

  return (
    <div>
      <fieldset>
        <legend>Demo 1</legend>
        <input type="text" onChange={hello} placeholder="Input your name" />
        <br />
        {result1}
      </fieldset>

      <fieldset>
        <legend>Demo 2</legend>
        Category <select onChange={selectCategory}>
          <option value="c1">Category 1</option>
          <option value="c2">Category 2</option>
          <option value="c3">Category 3</option>
          <option value="c4">Category 4</option>
        </select>
        <br />
        {result2}
      </fieldset>

      <fieldset>
        <legend>Demo 3</legend>
        Photo <input type="file" onChange={selectFile} />
        <br />
        <span dangerouslySetInnerHTML={{ __html: result3 }}></span>
      </fieldset>

      <fieldset>
        <legend>Demo 4</legend>
        Photos <input type="file" onChange={selectFiles} multiple={true} />
        <br />
        <span dangerouslySetInnerHTML={{ __html: result4 }}></span>
      </fieldset>

    </div>
  );
};

export default App;

Add Component to Entry File

Open index.js file in src folder and add new component to this file as below:

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import * as serviceWorker from './serviceWorker';

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

serviceWorker.unregister();

Structure of Project

Run Application

In Terminal windows in Visual Studio Code and type: npm start,
program will open url http://localhost:3000 on browser

Output