html 标签都叫 Dom
<head>
<meta charset="utf-8">
<title></title>
<script type="text/javascript">
</script>
</head>
<body>
<script type="text/javascript">
var arr1 = [1, 2, 3, 4, 5];
arr1.push(7)
console.log(arr1.length)
</script>
</body>
<body>
<script type="text/javascript">
var arr1 = [1, 2, 3, 4, 5];
arr1.push(7)
console.log(arr1.length)
</script>
</body>
<body>
# 要注意单双引号的问题
<button type="button" onclick="alert('11')"></button>
</body>
<body>
<a href="javascript:alert('nihao');">111</a>
</body>
<head>
<meta charset="utf-8">
<title></title>
<script type="text/javascript" src="1.js">
</script>
</head>