tweetBox.jsx

class TweetBox extends React.Component {
  constructor(){
    super()
    this.state = {
      text: "",
      photoAdded: false
    };
  }

  render() {
    let buttonText = this.state.photoAdded ? "Photo Added" : "Add Photo";
    
    return (
      <div className="well clearfix">
        <textarea 
          className="form-control"
          onChange={this.handleChange.bind(this)}></textarea>
      <br/>
       <button 
         className="btn btn-primary pull-right"
         disabled={this.state.text.length < 1 && !this.state.photoAdded}>
           Tweet 
         </button>
         <span>{remainingCharacters()}</span>
        <button 
          class="btn btn-default pull-right"
          onClick={this.handleClick.bind(this)}>{buttonText}</button>
     </div>
    );
  }

  remainingCharacters(){
    let sum = let sum = this.state.photoAdded ? 23 : 0;
    return 140 - this.state.text.length - sum;
  }

  handleClick(){
    this.setState({
      photoAdded: !this.state.photoAdded
    });
  }

  handleChange(e){
    let value = e.target.value;
    this.setState({
      text: value
    });
  }
}

ReactDOM.render(
  <TweetBox />,
  document.getElementById("container")
);