React - Input Element

Controlled component

The react forms components input accept a value attribute that is used to implement a controlled component.

A React form:

• written as a class component
• where the state is controlled by React (ie Controlled component)

class NameForm extends React.Component {
  constructor(props) {
    
    super(props);
    this.state = {value: 'DEFAULT'};

    // Mandatory binding of this.
    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
    
  }

  handleChange(event) {
    // toUppercase to enforce it
    console.log('handleChange was fired with the value '+event.target.value.toUpperCase());
    this.setState({value: event.target.value.toUpperCase()});
  }

  handleSubmit(event) {
    console.log('Your submitted name is: ' + this.state.value);
    event.preventDefault();
  }

  render() {
    return (
      <div>
      <p>Submit your name. It will be always uppercase and for each keystroke, the value attribute will be updated.</p>
      <form onSubmit={this.handleSubmit}>
        <label>
          Name:
          <input type="text" value={this.state.value} onChange={this.handleChange} />
        </label>
        <input type="submit" value="Submit" />
      </form>
      </div>
    );
  }
}

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

<div id="root"></div>

Uncontrolled Component

input example with a Uncontrolled Component using ref.

class NameForm extends React.Component {
  constructor(props) {
    super(props);
    this.handleSubmit = this.handleSubmit.bind(this);
    this.handleChange = this.handleChange.bind(this);
    this.input = React.createRef();
  }

  handleChange(event) {
    // Always uppercase :)
    console.log('handleChange was fired with the value '+this.input.current.value);
    this.input.current.value = this.input.current.value.toUpperCase();
  }
  
  handleSubmit(event) {
    console.log('The ref gives access to the HTML element via current: ' + this.input.current.__proto__.toString());
    console.log('where you have access to all HTML attribute such as the value');
    console.log('Example: the name submitted was: ' + this.input.current.value );
    event.preventDefault();
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label>
          Name:
          <input type="text" ref={this.input} defaultValue="ChangeMe"  onChange={this.handleChange} />
        </label>
        <input type="submit" value="Submit" />
      </form>
    );
  }
}

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

<div id="root"></div>