Cannot read property 'replace' of undefined

Question

function Addcategory() {
// Get the index number
var indexNo = $("#category-table > tr").length;
// Get the template row
var newRow = $("#category-table > tr:eq(0)").clone().prop('outerHTML');
// Reset the indexes on the template
newRow = newRow.replace(/_0_/g, "_" + indexNo + "_");
newRow = newRow.replace(/\[0\]/g, "[" + indexNo + "]");
// reset devextreme datepicker ids
newRow = newRow.replace(/devextreme0/g, "devextreme" + parseInt(2 * indexNo));
newRow = newRow.replace(/devextreme1/g, "devextreme" + parseInt(1 + 2 * indexNo));
// Append the row to the child table
$("#category-table").append(newRow);
// Make it visible
$("#category-table > tr:eq(" + indexNo + ")").removeClass("hidden");
$("#category-table > tr:eq(" + indexNo + ") > td:eq(8) > input").val("ADD");
$("#category-table > tr:eq(" + indexNo + ") > td:eq(0) > input").val("");
$("#category-table > tr:eq(" + indexNo + ") > td:eq(4) > select").next().remove();
}

 

<div class="card">
<div class="card-header">
<div class="row">
<div class="col">
<h3 class="card-title">Categories</h3>
</div>
<div class="col text-right">
<button title="Add tax category" id="add-category" class="btn btn-default btn-sm" type="button" onclick="Addcategory()"><i class="fa fa-plus"></i></button>
</div>
</div>
</div>
<div class="card-body">
<div id="categorieErrorMsg">
@Html.ValidationMessageFor(model => model.Categories, "", new { @class = "text-danger" })
</div>
<div id="category-values">
<table class="table table-condensed" id="category-table">
<thead>
<tr>
<th>@Html.DisplayNameFor(model => model.Categories.First().Name)</th>
<th>@Html.DisplayNameFor(model => model.Categories.First().InvoiceLabel)</th>
<th>@Html.DisplayNameFor(model => model.Categories.First().TaxRate)</th>
<th>@Html.DisplayNameFor(model => model.Categories.First().TaxCode)</th>
<th>@Html.DisplayNameFor(model => model.Categories.First().Attribute)</th>
<th>Valid value</th>
<th>@Html.DisplayNameFor(model => model.Categories.First().StartDate)</th>
<th>@Html.DisplayNameFor(model => model.Categories.First().EndDate)</th>
<th></th>
</tr>
</thead>
<tbody id="category-table">
@Html.EditorFor(model => model.Categories, new { htmlAttributes = new { @class = "form-control" } })
</tbody>
</table>
</div>
</div>
</div>