原因一：同时引入多版本layui
原因二：scripts写法错误：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8"/>
<title>登陆</title>
//layui样式引用
<link rel="stylesheet" href="/layui/css/layui.css" media="all">
</head>
<body>
<div id="wrapper">
<button id="test123">test</button>
</div>
//要加jquery引用和layui.js
<script src="/assets/libs/jquery-1.12.4/jquery.min.js"></script>
<script src="/layui/layui.js"></script>
<script type="application/javascript">
<script>
layui.use('layer', function () {
// layer = layui.layer;
var test123 = document.getElementById("test123");
test123.onclick = function () {
layer.msg("这是layui弹出层样式");
}
})
</script>
</body>
</html>
