The below code always outputs false to the console, and I have no idea why…

$(document).on('change', '#<%= checkSetSmtpCredentials.ClientID %>', () => {
    let isChecked = $(this).is(':checked');
    console.log(isChecked); <-- always false

    // code omitted for brevity
});

If it matters, this is a ASP.NET Framework WebForms app, hence the <%= checkSetSmtpCredentials.ClientID %>. Jquery version is 2.1.3. No, upgrading is not an option right now.