IE6/7中获取Button元素的值的bug

如下

<button value="abc">测试</button>
<script>
	var btn = document.getElementsByTagName('button')[0];
	alert(btn.value);
	alert(btn.getAttribute('value'));
</script>

IE6/7:

IE8/9/10/Firefox/Safari/Chrome/Opera:

IE6/7 中返回的是innerHTML，实现错误。用getAttributeNode修复，如下

<button value="abc">测试</button>
<script>
	var btn = document.getElementsByTagName('button')[0];
	alert(btn.getAttributeNode('value').nodeValue);
</script>