How to convert string into date while setting custom filters in jquery grid?

Question

This is one of the columns in my grid-

{ name: 'DueDate',
            index: 'DueDate',
            sortable: true,
            sorttype: 'date',
            editable: false,
            width: 125,
            formatter: 'date',
            searchoptions: {
                dataInit: function(element) {
                    $(element).datepicker({
                       dateFormat: 'mm/dd/yy'
                    });
                }
            }
        }

I am trying to setup a custom filter like this-

 var now = moment();
    var formattedDate = now.format('MM/DD/YYYY');
    var date = Date.parse(formattedDate);
    var f = { groupOp: "OR", rules: [] };
    f.rules.push({ field: 'DueDate', op: 'lt', data: date});
    $grid[0].p.search = true;
    $.extend($grid[0].p.postData, { filters: JSON.stringify(f) });
    $grid.trigger('reloadGrid');

'DueDate' returned is a date string. so i need to parse it before i can compare. How do i do this? Is there even a way to do it?

UPDATE:

DueDate is a Datetime object and the value from the controller is /Date(-62135568000000)/(json object) This is formatted into 'mm/dd/yy' format and this converts to a date string and looks like normal date. I have a drop down menu item with all the filter criteria. I click on one of the menu-items, which is to select all the rows that have DueDate < Today's date for which i need to parse 'DueDate' field's value.

For Testing, when i use this-

 var now = moment();
    var formattedDate = now.format('MM/DD/YYYY');
    var rowdata = $grid.jqGrid('getRowData');
    var dueDate = rowdata[0].DueDate; //just picking first row's due date
    alert("DueDate: " + dueDate);//alerts "1/1/2015"   
    var d = Date.parse(formattedDate);
    //var ts = dueDate.getTime(); --I get an error here- getTime() not supported for this object.
   //this works fine- & I need something like this for filters
    if (Date.parse(dueDate) < d) {
        alert("It is due");
    }
    var f = { groupOp: "AND", rules: [] };
    f.rules.push({ field: 'DueDate', op: 'lt', data: d });
    f.rules.push({ field: 'HasMapping', op: 'eq', data: true });
    $grid[0].p.search = true;
    $.extend($grid[0].p.postData, { filters: JSON.stringify(f) });
    $grid.trigger('reloadGrid');