后面三个undefined是怎样输出来的

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<div id="box">
			<ul>
				<li>111</li>
				<li>222</li>
				<li>333</li>
				<li>444</li>
				<li>555</li>
			</ul>
		</div>
		
		<script type="text/javascript">
			var oUl = document.querySelector('ul');
			
			for(var i in oUl.children){
				document.write(oUl.children[i].innerHTML);//111222333444555undefinedundefinedundefined
			}
		</script>
	</body>
</html>

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3条回答默认最新

qq_25376897 2020-11-30 14:11

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<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<div id="box">
			<ul>
				<li>111</li>
				<li>222</li>
				<li>333</li>
				<li>444</li>
				<li>555</li>
			</ul>
		</div>
		
		<script type="text/javascript">
			var oUl = document.querySelector('ul');
			
			for(var i=0;i<oUl.children.length;i++){
				document.write(oUl.children[i].innerHTML);//111222333444555
			}
		</script>
	</body>
</html>

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