js运行的时候，想用内循环为tr标签增加td标签，但内循环始终无法执行
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>动态数据表格</title>
<style>
table{
width: 300px;
margin: 100px auto;
}
th{
background-color:rgb(145, 141, 141);
font-size: 20px;
}
</style>
</head>
<body>
<table border="1" cellspacing='0'>
<thead>
<tr>
<th>姓名</th>
<th>科目</th>
<th>分数</th>
</tr>
</thead>
<tbody>
</tbody>
</table>
<script>
var datas=[
{
name:'小米',
subject:'javascript',
grade:'100'
},{
name:'小红',
subject:'python',
grade:'49'
},{
name:'小明',
subject:'java',
grade:'86'
}
]
var tbody=document.getElementsByTagName('tbody')[0]
for(i=0;i<datas.length;i++){
var tr = document.createElement('tr')
tbody.appendChild(tr)
for(k=0;k<datas[i].length;k++){
console.log(i)
var td = document.createElement('td')
tr.appendChild(td)
}
}
</script>
</body>
</html>
