JavaScript switch 语句只执行默认情况 [英] JavaScript switch statement only executes the default case
本文介绍了JavaScript switch 语句只执行默认情况的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我是 JavaScript 的新手，编写了这个简短的脚本来为我的页面正文选择一种随机的背景颜色，但它只会继续执行默认情况.我不知道有什么问题.
I'm new to JavaScript and wrote this short script to choose a random background color for the body of my page, but it only keeps executing the default case. I don't know what's the problem.
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<script>
function chC(){
var cl=document.getElementById('demo');
var colNo=Math.random()*4;
switch (colNo){
case 1:{
cl.style.background='red';
}
case 2:{
cl.style.background='yellow';
}
case 3:{
cl.style.background='pink';
}
default :{
cl.style.background='orange';
}
}
}
</script>
<title></title>
</head>
<body id="demo">
<button type="button" onclick="chC();">change</button>
</body>
</html>
推荐答案
Math.random() * 4 不返回 1, 2code> 或 3，它返回类似
Math.random() * 4 doesn't return 1, 2 or 3, it returns things like
3.4111702758818865
3.9287009509280324
1.1707445457577705
1.5766741186380386
2.6374688586220145
你需要四舍五入，因为你不包括零，我猜你想上升，但这也会包括4，所以谁知道
You need to round that, and as you're not including zero, I guess you want to go up, but that would include 4 as well, so who knows
var colNo = Math.ceil( Math.random()*4 ); // 1-4
// or
var colNo = Math.floor( Math.random()*4 ); // 0-3
而且....你的开关/外壳有问题，你需要在满足条件时断开
And.... your switch/case is faulty, you need to break when a condition is met
switch (colNo) {
case 1:
cl.style.background = 'red';
break;
case 2:
cl.style.background = 'yellow';
break;
case 3:
cl.style.background = 'pink';
break;
default:
cl.style.background = 'orange';
}
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