<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(runoob.com)</title>
</head>
<body>
<p>本例调用的函数会执行一个计算，然后返回结果：</p>
<p id="demo">0</p>
<button onclick="add()">点我+1</button>
<button onclick="del()">点我-1</button>
<p id="sum">0</p>
<script>
function add(){
var x=document.getElementById("demo").innerHTML;
if(x<10)
x=x*1+1;
else x=x*1;
document.getElementById("demo").innerHTML=x;
document.getElementById("sum").innerHTML=x*30;
}
function del(){
var x=document.getElementById("demo").innerHTML;
if(x>0)
x=x*1-1;
else x=x*1;
document.getElementById("demo").innerHTML=x;
document.getElementById("sum").innerHTML=x*30;
}
</script>
</body>
</html>
![在这里插入图片描述]()
