Right now we use codemirror's JavaScript mode on the website but there's a JSX mode now so we should start using that instead.

var isJS = this.state.mode === this.MODES.JS;
    var compiledCode = '';
    try {
      compiledCode = this.compileCode();
    } catch (err) {}
    var JSContent =
      <CodeMirrorEditor
        key="js"
        className="playgroundStage CodeMirror-readonly"
        onChange={this.handleCodeChange}
        codeText={compiledCode}
        readOnly={true}
        lineNumbers={this.props.showLineNumbers}
      />;
    var JSXContent =
      <CodeMirrorEditor
        key="jsx"
        onChange={this.handleCodeChange}
        className="playgroundStage"
        codeText={this.state.code}
        lineNumbers={this.props.showLineNumbers}
      />;
    var JSXTabClassName =
      'playground-tab' + (isJS ? '' : ' playground-tab-active');
    var JSTabClassName =
      'playground-tab' + (isJS ? ' playground-tab-active' : '');
    var JSTab =
      <div
        className={JSTabClassName}
        onClick={this.handleCodeModeSwitch.bind(this, this.MODES.JS)}>