<script type="text/javascript">

layui.use(['layer'], function(){

$ = layui.juqery;

  layer = layui.layer;

});

function dologin(){

var username = $('#username').val();

var pwd = $('#pwd').val();

var verifycode = $('#verifycode').val();

if (username == '') {

layer.alert('请输入用户名',{icon:2});

return;

}

if (pwd == '') {

layer.alert('请输入密码',{icon:2});

return;

}

if (verifycode == '') {

layer.alert('请输入验证码',{icon:2});

return;

}

}

</script>

报错：Uncaught TypeError: $ is not a function