1. 获取html标签内容 --innerHTML
2. 获取标签本身与内容 --outerHTML
<!DOCTYPE html>
<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>Document</title>
</head>
<body>
<p id="demo">替换 “Microsoft” 为 “Runoob”：<span>haha</span></p>
<script>
var str = document.getElementById("demo");
console.log("innerHTML打印结果：" + str.innerHTML)
console.log("outerHTML打印结果：" + str.outerHTML)
</script>
</body>
</html>
</script>
