javascript - react-codemirror怎么添加代码折叠功能？

Question

github下的example例子下进行添加代码行高亮成功，但代码折叠的功能没有效果

var React = require('react');
var ReactDOM = require('react-dom');
var Codemirror = require('../../src/Codemirror');

require('codemirror/mode/javascript/javascript');
require('codemirror/mode/xml/xml');
require('codemirror/mode/markdown/markdown');
// 添加高亮
require('codemirror/addon/selection/active-line');
require('codemirror/addon/fold/foldcode');
require('codemirror/addon/fold/foldgutter');

var defaults = {
    markdown: '# Heading\n\nSome **bold** and _italic_ text\nBy [Jed Watson](https://github.com/JedWatson)',
    javascript: 'var component = {\n\tname: "react-codemirror",\n\tauthor: "Jed Watson",\n\trepo: "https://github.com/JedWatson/react-codemirror"\n};'
};

var App = React.createClass({
    getInitialState () {
        return {
            code: defaults.markdown,
            readOnly: false,
            mode: 'markdown',
        };
    },
    updateCode (newCode) {
        this.setState({
            code: newCode
        });
    },
    changeMode (e) {
        var mode = e.target.value;
        this.setState({
            mode: mode,
            code: defaults[mode]
        });
    },
    toggleReadOnly () {
        this.setState({
            readOnly: !this.state.readOnly
        }, () => this.refs.editor.focus());
    },
    interact (cm) {
        console.log(cm.getValue());
    },
    render () {
        var options = {
            styleActiveLine: true,
            lineNumbers: true,
            lineWrapping: true,
            mode: this.state.mode,
            foldGutter: true,
        gutters: ["CodeMirror-linenumbers", "CodeMirror-foldgutter"]
        };
        return (
            <p>
                <Codemirror ref="editor" value={this.state.code} onChange={this.updateCode} options={options} interact={this.interact} />
                <p style={{ marginTop: 10 }}>
                    <select onChange={this.changeMode} value={this.state.mode}>
                        <option value="markdown">Markdown</option>
                        <option value="javascript">JavaScript</option>
                    </select>
                    <button onClick={this.toggleReadOnly}>Toggle read-only mode (currently {this.state.readOnly ? 'on' : 'off'})</button>
                </p>
            </p>
        );
    }
});

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

样式已经在example.css引进去了

.ReactCodeMirror {
    border: 1px solid #ccc;
}

@import (inline) "../../node_modules/codemirror/lib/codemirror.css";
@import (inline) "../../node_modules/codemirror/addon/fold/foldgutter.css";

但效果如下：

并没有出现左侧的小三角，求各位大侠解答，谢谢！！