<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
.box {
200px;
height: 200px;
line-height: 200px;
background-color: #ccc;
font-size: 30px;
text-align: center;
}
</style>
</head>
<body>
<div class="box">此乃点名器</div>
<input type="button" value="点名" id="btn">
<!-- <button id="btn">点名</button> -->
<script>
var btn = document.getElementById("btn");
var box = document.getElementsByClassName("box")[0];
// 3、写一个随机抽名的案例？（点击按钮开启定时器，
// 定时器中去随机抽取人名，把全班的人放在一个数组中，只要想办法获取随机的索引号就可以）
btn.onclick = function() {
if(this.value==="点名") {
function fn() {
var arr = ["张三","李四","王五","赵六","黑七","白八","紫九","红薯"];
var index = parseInt(Math.random()*arr.length);
var n1 = parseInt(Math.random()*255+1);
var n2 = parseInt(Math.random()*255+1);
var n3 = parseInt(Math.random()*255+1);
box.style.background ="rgb("+n1+","+n2+","+n3+")" ;
box.innerHTML = arr[index];
}
this.value = "停止";
//定时器不加var声明，涉及到作用域问题
timer=setInterval(fn,2);
}else {
clearInterval(timer);
this.value = "点名";
}
}
</script>
</body>
</html>