React 表单refs

<!DOCTYPE html>
<html>
<head >
<meta charset="UTF-8">
<title></title>
<script src="js/react.js"></script>
<script src="js/react-dom.js"></script>
<script src="js/browser.min.js"></script>
</head>
<body>
<div ref='num2'/>
<br/>
<button onClick={this.handleClick}>求和</button>
</div>
}
})
ReactDOM.render(
<MyComponent/>,
document.getElementById('example')
)
</script>
</body>
</html>