如下：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>JavaScript计算值</title>
</head>
<body>
<p>假设y=5,计算x=y+2,并显示结果.</p>
<button type="button" onclick="myFunction()">点击这里</button>
<p id="pid"></p>
<script>
function myFunction()
{
var y=5;
var x=y+2;
var demoP=document.getElementById("pid");
demoP.innerHTML="x="+x;
}
</script>
</body>
</html>
