the problem was 

$("#dialog-QS-table").jqGrid('footerData', y);

should have been 

$("#dialog-QS-table").jqGrid('footerData','set', y);

i have the following table

UOM Type Matrix Quantity Cost_Rate Value

Repetitions 0.00 0.00 0.00 0.00

100% 0.00 0.00 0.00 0.00

XTranslated 0.00 0.00 0.00 0.00

95-99% 0.00 0.00 0.00 0.00

85-94% 0.00 0.00 0.00 0.00

75-84% 0.00 0.00 0.00 0.00

50-74% 0.00 0.00 0.00 0.00

<=50% 0.00 1111.00 0.00 0.00

Totals: 1111.00 0.00 0.00

with the following options

var opts = { autowidth: true, height: 'auto', viewrecords: true, sortorder: "desc", multiselect: false, caption: "Quantity Split", colNames: ['UOM Type', 'Matrix', 'Quantity', 'Cost Rate', 'Value'], colModel: [ { name: 'UOM_Type', align: 'left', editable: false, footervalue: 'Hi' }, { name: 'Matrix', align: 'left', editable: false }, { name: 'Quantity', align: "right", formatter: 'number', editable: true }, { name: 'Cost_Rate', align: "right", formatter: 'number', editable: true }, { name: 'Value', align: "right", formatter: 'number', editable: true } ], altRows: true, footerrow: true, userDataOnFooter: true };

but when i call the function

var y = $("#dialog-QS-table").jqGrid('footerData'); y['UOM_Type'] = "HI"; $("#dialog-QS-table").jqGrid('footerData', y);

it seems to throw an error saying "TypeError Object doesnt support property or method toLowerCase" the grid itself is created but the footer is blank can anyone help please.