Uncaught SyntaxError: Invalid or unexpected token

Cześć,
Otrzymuję w konsoli unexpected token mimo iż kod mam w jednej linii, co może być tego przyczyną?

<script type="text/javascript">
        $(document).ready(function () {
            $("#add-row").click(function () {
                markup = '<tr><td>' + '@(Html.DropDownListFor(p => p.ProductID, new SelectList(Model.Products, "Id", "ProductName"), "--Wybierz produkt--", new { @class = "form-control" }))+</td><td><input asp-for="Quantity" class="form-control" placeholder="Ilość" /></td></tr>'
                tableBody = $("table tbody");
                tableBody.append(markup);
            });
        });
</script>

Wrzuć fragment wyrenderowanego kodu, a nie templatki z C#.

Wyrenederowany kod poniżej

<script type="text/javascript">
        $(document).ready(function () {
            $("#add-row").click(function () {
                markup = '<tr><td>' + '<select class="form-control" data-val="true" data-val-required="The ProductID field is required." id="ProductID" name="ProductID"><option value="">--Wybierz produkt--</option>
<option value="4">Mleko 1,5%</option>
<option value="5">P&#x142;atki owsiane</option>
<option value="6">P&#x142;atki kukurydziane</option>
<option value="7">Truskawki</option>
<option value="8">Ser chudy</option>
</select>+</td><td><input asp-for="Quantity" class="form-control" placeholder="Ilość" /></td></tr>'
                tableBody = $("table tbody");
                tableBody.append(markup);
            });
        });
</script>

Wielowierszowe stringi trzeba oznaczać ([template literals](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals), to ten klawisz nad tabem), a nie zwykłymi ' , lub " `.
Czyli:

<script type="text/javascript">
        $(document).ready(function () {
            $("#add-row").click(function () {
                markup = '<tr><td>' + `<select class="form-control" data-val="true" data-val-required="The ProductID field is required." id="ProductID" name="ProductID"><option value="">--Wybierz produkt--</option>
<option value="4">Mleko 1,5%</option>
<option value="5">P&#x142;atki owsiane</option>
<option value="6">P&#x142;atki kukurydziane</option>
<option value="7">Truskawki</option>
<option value="8">Ser chudy</option>
</select>+</td><td><input asp-for="Quantity" class="form-control" placeholder="Ilość" /></td></tr>`;
                tableBody = $("table tbody");
                tableBody.append(markup);
            });
        });
</script>