For one of the columns in my jqGrid, I'm providing a custom formatter function. I'm providing some special cases, but if those conditions aren't met, I'd like to resort to using the built-in date formatter utility method. It doesn't seem that I'm getting the right combination of $.extend() to create the options that method is expecting.

My colModel for this column:

{ name:'expires', 
    index:'7',
    width:90,
    align:"right",
    resizable: false,
    formatter: expireFormat,
    formatoptions: {srcformat:"l, F d, Y g:i:s A",newformat:"n/j/Y"}
},

And an example of what I'm trying to do

function expireFormat(cellValue, opts, rowObject) {
    if (cellValue == null || cellValue == 1451520000) {
        // a specific date that should show as blank
        return '';
    } else {
        // here is where I'd like to just call the $.fmatter.util.DateFormat
        var dt = new Date(cellValue * 1000);
        var op = $.extend({},opts.date);
        if(!isUndefined(opts.colModel.formatoptions)) {
            op = $.extend({},op,opts.colModel.formatoptions);
        }
        return $.fmatter.util.DateFormat(op.srcformat,dt,op.newformat,op);
    }
}

(An exception is being thrown in the guts of that DateFormat method, looks like where it's trying to read into a masks property of the options that get passed in)

EDIT:

The $.extend that put everything in the place it needed was getting it from that global property where the i18n library set it, $.jgrid.formatter.date.

var op = $.extend({}, $.jgrid.formatter.date);
if(!isUndefined(opts.colModel.formatoptions)) {
    op = $.extend({}, op, opts.colModel.formatoptions);
}
return $.fmatter.util.DateFormat(op.srcformat,dt.toLocaleString(),op.newformat,op);