表单验证提交按钮

Question

因此，我正在尝试禁用“提交”按钮，直到选择了礼品券为止。我该怎么办？这是一些上下文的代码段。我正在使用PHP Symfony 2.8。因此，这是我项目中的.twig文件。

<div class="grid_7 alpha omega data-field" style="width:260px;">
        <div class="grid_3 alpha omega">Amount</div>
                                <div class="grid_4 alpha omega">
                                    <select class="claim" name="gc-claim-voucher" style="width:145px;">
                                        <option value="" <%= !claim.voucher || claim.voucher == "" || claim.voucher == "undefined" ? 'selected="selected"' : '' %> >None</option>
                                        <option value="GC_AMAZON_100" <%= claim.voucher && claim.voucher == "GC_AMAZON_100" ? 'selected="selected"' : '' %> >100</option>
                                        <option value="GC_AMAZON_50" <%= claim.voucher && claim.voucher == "GC_AMAZON_50" ? 'selected="selected"' : '' %> >50</option>
                                    </select>
                                </div>
                            </div>

                        </div>
                    <% }) %>
                    <a href="javascript: void 0;" class="send-voucher link">Submit</a>
                    <a class="button small voucher-communication-logs">Voucher Communication Logs</a>
                <% } else { %>
                    <div class="detail-body grid_7 alpha omega">
                            <a href="javascript: void 0;" class="add-claim link">+ Add new claim</a>
                    </div>
                <% } %>
            </div>

        </div>