declarative react example

dog-survey.html

<script src="https://unpkg.com/react@15.3.1/dist/react.js"></script>
<script src="https://unpkg.com/react-dom@15.3.1/dist/react-dom.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-core/5.8.24/browser.min.js"></script>

<title>React</title>
<div id="app"></div>

<script type="text/babel">
  class App extends React.Component {
    constructor() {
      super();
      this.state = { dogName: '', hasDog: null, output: null };
      this.updateHasDog = this.updateHasDog.bind(this);
      this.updateDogName = this.updateDogName.bind(this);
      this.onSave = this.onSave.bind(this);
    }

    onSave() {
      let formData = {
        hasDog: this.state.hasDog,
        dogName: this.state.dogName
      };

      this.setState({ output: JSON.stringify(formData) });
    }

    updateHasDog({ target }) {
      this.setState({ hasDog: target.value === "yes" });
    }

    updateDogName({ target }) {
      this.setState({ dogName: target.value });
    }

    isValid() {
      return !this.state.hasDog ||
             (this.state.hasDog && this.state.dogName);
    }

    render() {
      return (
        <div>
          <p>Do you have a dog?</p>

          <label>
            <input onChange={this.updateHasDog}
                   name="hasDog"
                   type="radio"
                   value="yes" />{' '}
            Yes
          </label>

          <label>
            <input onChange={this.updateHasDog}
                   name="hasDog"
                   type="radio"
                   value="no" />{' '}
            No
          </label>

          <br/><br/>

          {this.state.hasDog && (
            <div>
              <label>What is the name of your dog?</label><br />
              <input onChange={this.updateDogName} value={this.state.dogName} />
            </div>
          )}

          <br/>

          <button onClick={this.onSave} disabled={!this.isValid()}>Save</button>
          <div>{this.state.output}</div>
        </div>
      );
    }
  }

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