<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<input type="text" id="uname">
<button onclick="btnValidate()">验证</button>
<div id="uname-show"></div>
<script src="common.js"></script>
<script>
function btnValidate(){
//1、获取uname的value的长度
var len = $("uname").value.length;
//2、验证长度是否在6-18位之间
if(len>=6 && len <= 18){
$("uname-show").innerHTML = "通过";
$("uname-show").style.color="green";
}else{
$("uname-show").innerHTML = "用户名必须在6-18位之间";
$("uname-show").style.color='red';
}
}
</script>
</body>
</html>
原文：https://www.cnblogs.com/-hjj/p/9943398.html