我的建议是:

$(function () {
  $(".fa-update").on("click", function (e) {
    var data = {};
    var currentRowParams = $(this).closest("tr").find('input').each(function(index, element) {
      var name = element.name ? element.name : 'undefined' + index;
      data[name] = element.value || '';
    });
    var x =  JSON.stringify(data);
    console.log(x);
    
    //
    // If instead you want the params in a traditional GET
    //
  });
});

<script src="https://code.jquery.com/jquery-1.12.4.min.js"></script>

<table>
    <tbody>
    <tr>
        <td>@Html.TextBox("codeTextBox", discount.Code) </td>
        <td><input type="checkbox" name="freeShippingCheckBox" id="freeShippingCheckBox" checked="@discount.FreeShipping" /> </td>
        <td><input type="tel" value="Ta 3 betala for 2" readonly /></td>
        <td><input type="checkbox" id="activeCheckBox" name="activeCheckBox" checked="@discount.Active" /></td>
        <td><input type="datetime" value="@discount.CreatedDate" readonly /></td>
        <td>
            <input type="button" value="Radera" class="fa fa-remove" data-url="@Url.Action("DeleteDiscountCode","Discount",new { id= discount.Id})" />
            <input type="button" value="Uppdatera" class="fa fa-update" data-url="@Url.Action("UpdateDiscount","Discount",new { id= discount.Id, })" />
            <input type="button" value="Produkter" class="fa fa-products" />
        </td>
        <input id="@discount.Id.ToString()" type="hidden" value="@discount.Id" />
    </tr>
    </tbody>
</table>