updated the accept an config like below:

stressTest.config = {
    event: "complete",
    setup: function(){
        $firstCell = $(".row.item:first input.cell_box:first");
        $lastCell = $(".row.item:first input.cell_box:last");
    },
    callbackOdd: function(opts){
        $firstCell.focus().trigger(stressTest.config.event);
    },
    callbackEven: function(opts){
        $lastCell.focus().trigger(stressTest.config.event);
    },
    times: 500,
    eventContext: document.getElementsByTagName("body")
};