x
 
<!DOCTYPE html>
<html>
<body>
<h1>JavaScript 数字</h1>
<p>一个常见的错误是期望这个结果为 30:</p>
<p id="demo"></p>
<script>
var x = 10;
var y = 20;
document.getElementById("demo").innerHTML = "结果是:" + x + y;
</script>
</body>
</html>