<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>练习</title>
<script type="text/javascript" src="learn.js">
//document.write('js练习。');//分号;可省。1.可写在body里；2.可写在head里；3.可从外部引入js文件。
</script>
</head>
<body>
<input type="button" name="js练习" value="普通按钮" onclick="alert('从零开始')">
</body>
</html>
document.write('从js文件中引入。')
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>练习</title>
<script type="text/javascript" src="learn.js">
//document.write('js练习。');//分号;可省。1.可写在body里；2.可写在head里；3.可从外部引入js文件。
</script>
</head>
<body>
<input type="button" name="js练习" value="普通按钮" onclick="alert('从零开始')">
<script type="text/javascript">
document.write('普通文本,<h1>h1标题</h1>这里会换行;<br>再一个换行;<br/> <ul><li>列表1</li><li>列表2</li></ul>');
alert('直接弹出');
</script>
</body>
</html>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>练习</title>
</head>
<body>
<script type="text/javascript">
var x=10;
var y;
y=11;
// alert(x);
// alert(y);
var a=10,b=20,c=30;
// alert(a+b+c);
</script>
<script type="text/javascript">
document.write("a+b+c="+(a+b+c));
</script>
</body>
</html>
