<link rel="stylesheet" href="~/lib/bootstrap4-toggle-3.4.0/css/bootstrap4-toggle.css" />
<script src="~/lib/bootstrap4-toggle-3.4.0/js/bootstrap4-toggle.js"></script>

<input type="checkbox" checked data-toggle="toggle" data-onstyle="outline-success" data-offstyle="outline-danger" id="testToggle">

$(document).ready(function () {
    $('.my-checkbox').change(function () {
        alert($(this).prop('checked'))
    });

    $(".custom-control-input").change(function () {
        if (this.checked) {
            alert($(this).val());
        }
    });
})
}

<div class="container">
    <label>
        <input type="checkbox" name="my-checkbox" class="my-checkbox">Some caption
    </label>

    <div id="hideableDiv" class="hiddenByDefault">
        Some hidable content
    </div>
</div>