"undefined is not a function" in jqgrid

Question

In JQgrid for delete operation, I'm using this deldata to send the key value to the server.

               delData: {
                dnis: function () {
                    var sel_id = $('#jQGridDemo').jqGrid('getGridParam', 'selrow');
                    var value = $('#jQGridDemo').jqGrid('getCell', sel_id, 'DNIS');
                    return value;
                }

In the same way, to reload the grid after add, I'm using this nippet.

              afterSubmit: function (response, postdata) {
                $("#jQGridDemo").jqGrid('setGridParam', { datatype: 'json' }).trigger('reloadGrid');
                return [false, response.responseText]
                },

But everywhere on using $("#jQGridDemo").jqGrid( i get this following error

Uncaught TypeError: undefined is not a function

I spent my full day, but couldn't find the reason of the problem.

I'm using this grid in MVC cshtml razor view.

This is similar to this question. Please help me out.