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 function component
• where the state is controlled by React (ie Controlled component)

const NameForm = function(){

  const [name, setName] = React.useState('DEFAULT');


  const handleChange = function(event) {
    // toUppercase to enforce it
    console.log('handleChange was fired with the value '+event.target.value.toUpperCase());
    setName(event.target.value.toUpperCase());
  }

  const handleSubmit = function(event) {
    console.log('Your submitted name is: ' + name);
    event.preventDefault();
  }

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

We are using a ref to get the value back as example but you could also use the event to get the value.

const NameForm = function() {

  const input = React.useRef();

  const handleChange = function(event) {
    // Always uppercase :)
    console.log('handleChange was fired with the value via the event to '+event.target.value);
    // The ref gives access to the HTML element via current
    console.log('handleChange was fired with the value via the dom ref element '+input.current.value);
  }
  
  const handleSubmit = function(event) {
    console.log('The ref gives access to the HTML element via current. Ref Proto: ' + 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: ' + input.current.value);
    event.preventDefault();
  }


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

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

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