安装：
npm install classnames

功能：
将true的class 显示出来，false 的隐藏

参考文档：https://manofhustle.com/2015/01/19/dynamically-add-classes-react-classset/

demo:

var classNames = require('classnames');
var HelloWorld = React.createClass({
    render: function () {
        var classes = classNames({
            "important": true,"normal": true,"noclass":false
        });
        return <div>
            <input type="text" className={classes}/>
        </div>
    }
})