Notifications
JavaScript
FD.Page.showErrorCallback = function (data, event) {
    notify.alert('Client Side Error.');
};

FD.Page.showWarningCallback = function (data, event) {
    notify.info('Client Side Warning.');
};

FD.Page.showPersistentWarningCallback = function (data, event) {
    notify.info('Persistent Client Side Warning.', true);
};
Automatic $.fdAjax Error
JavaScript
FD.Page.handleMakeError = function (data, event) {
    $.fdAjax({
        url: baseUrl + "MakeError",
        callback: function (result) {
            if (!result.data) {
                // Do error cleanup here
            }
        }
    });
}

FD.Page.handleMakeException = function (data, event) {
    $.fdAjax({
        url: baseUrl + "MakeException",
        callback: function (result) {
            if (!result.data) {
                // Do error cleanup here
            }
        }
    });
}
C#
public IActionResult MakeError()
{
    return Error("This is a server side error message.");
}

public IActionResult MakeError()
{
    return Error("This is a server side error message.");
}
Automatic Unobtrusive Ajax Error
This also works on forms and has other data-ajax calbacks.
HTML
<div class="btn-group">
    <a class="btn btn-primary" data-fd-control="button" asp-action="MakeError">Button</a>
    <a class="btn btn-secondary" data-fd-control="button" asp-action="MakException">Button</a>
</div>
C#
public IActionResult MakeError()
{
    return Error("This is a server side error message.");
}

public IActionResult MakeError()
{
    return Error("This is a server side error message.");
}