根据验证结果切换元素可见性

Question

Given the following HTML

<form class="form-horizontal"
      asp-controller="Installation"
      asp-action="CreateUser"
      method="post">
    <fieldset>

        <!-- Form Name -->
        <legend>Account Creation</legend>

        <!-- Username input-->
        <div class="form-group">
            <label class="col-md-4 control-label" for="userName">Username</label>
            <div class="col-md-4">
                <input id="UserName" name="UserName" asp-for="UserName" type="text" placeholder="Username" class="form-control input-md" required="">
                <span id="usernameTip" class="help-block hidden">Enter a unique Username</span>
                <span class="has-error" asp-validation-for="UserName"></span>
            </div>
        </div>

        <!-- Email input-->
        <div class="form-group">
            <label class="col-md-4 control-label" for="email">E-mail</label>
            <div class="col-md-4">
                <input id="email"
                       name="email"
                       type="text"
                       placeholder="jane@doe.com"
                       class="form-control input-md"
                       required=""
                       asp-for="Email">
                <span class="help-block">Enter your e-mail address</span>
            </div>
        </div>

        <!-- Password input-->
        <div class="form-group">
            <label class="col-md-4 control-label" for="password">Password</label>
            <div class="col-md-4">
                <input id="password"
                       name="password"
                       type="password"
                       placeholder="password"
                       class="form-control input-md"
                       required=""
                       asp-for="Password">
                <span class="help-block">Enter a password that is at least 8 characters, fewer than 30</span>
            </div>
        </div>

        <!-- Password input-->
        <div class="form-group">
            <label class="col-md-4 control-label" for="confirmPassword">Confirm Password</label>
            <div class="col-md-4">
                <input id="confirmPassword"
                       name="confirmPassword"
                       type="password"
                       placeholder="password"
                       class="form-control input-md"
                       required=""
                       asp-for="PasswordConfirmation">
                <span class="help-block">Re-enter your password</span>
            </div>
        </div>

        <!-- Submit -->
        <div class="form-group">
            <label class="col-md-4 control-label"
                   for="createAccount"></label>
            <div class="col-md-4">
                <button id="createAccount" type="submit" name="createAccount" class="btn btn-primary">Create Account</button>
            </div>
        </div>

    </fieldset>
</form>

I would like to hide/show the usernameTip span, when the asp-validation-for span contains a validation error, along with any other span that i'm using as a tip when there is an adjacent asp-validation-for span.

Reading this post I can get the JavaScript needed to show/hide the span. The only thing I can't figure out is if the View actually has knowledge of the validation errors in a manor that lets me conditionally hide/show that usernameTip span if errors exist.

Does anyone know what I need to do in order to toggle the visibility based off the data annotation errors on my model?

When looking in Chrome, asp-validation-for span is turned into this at compile time:

<span class="has-error field-validation-error" data-valmsg-for="UserName" data-valmsg-replace="true">Usernames must be between 2 and 50 characters</span>

EDIT

When validation fails, there is a ==$0 appended to the end.

Usernames must be between 2 and 50 characters == $0

I do not see any classes being added or removed from the span when the validation fails.

Edit 2

I got this working using the accepted answer. For those looking in the future however, you can use MVC's ViewData property in the view to determine if there are errors.

<div class="col-md-4">
    <input id="UserName" name="UserName" asp-for="UserName" type="text" placeholder="Username" class="form-control input-md" required="">
    @if (ViewData.ModelState[nameof(AccountCreationViewModel.UserName)] == null || ViewData.ModelState[nameof(AccountCreationViewModel.UserName)].Errors.Count == 0)
    {
        <span class="help-block">Enter a unique Username</span>
    }
    else
    {
        <span class="label label-danger" role="alert" asp-validation-for="UserName"></span>
    }
</div>

Answer 1

<div class="col-md-4">
    <input id="UserName" name="UserName" asp-for="UserName" type="text" placeholder="Username" class="form-control input-md" required="">
    <span id="usernameTip" class="help-block hidden">Enter a unique Username</span>
    <span id="error" class="has-error" asp-validation-for="UserName"></span>
</div>
    <script>

   if( $("#error").text().length>0){
//show usernameTip 
}
</script>