参考代码自己改改，用了jQuery
<!doctype html><html>
<head>
<meta charset="utf-8">
<title></title>
<script type="text/javascript" src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
<script type="text/javascript">
$(function(){
$('.btn').click(function(){
alert($(this).parent().parent().find('td:eq(0)').attr('val'))
})
})
</script>
</head>
<body>
<table id="tab">
<tr>
<td val="1">111</td><td>6666</td><td><input type="button" class="btn" value="button"></td>
</tr>
<tr>
<td val="2">111</td><td>6666</td><td><input type="button" class="btn" value="button"></td>
</tr>
</table>
</body>
</html>
