Javascript Arrow Keypress

function fireKey(el)
{
    var key;
    switch(el)
    {
        case "left":
        key = 37;
        break;
        case "right":
        key = 39;
        break;
        case "up":
        key = 38;
        break;
        case "down":
        key = 40;
    }

    if(document.createEventObject) {
        var eventObj = document.createEventObject();
        eventObj.keyCode = key;
        el.fireEvent("onkeydown", eventObj);
    } else if(document.createEvent) {
        var eventObj = document.createEvent("Events");
        eventObj.initEvent("keydown", true, true);
        eventObj.which = key;
        document.body.dispatchEvent(eventObj);
    }
}