calling setinterval with object reference

I have a banner rotator and I wanted to use objects instead of functions so I could make the code more efficient. Anyway I can't seem to get setInterval to work. I think it's got something to do with the object reference. Can anybody explain this? Here's what I've got so far:

window.addEvent('domready', function() {
function set_banner(divid, array)
{
    var banner = $(divid);
    banner.set('html', '<a href=""><img src="" alt=""/></a>');
    var banner_link = $(divid).getElement('a');
    var banner_image = $(divid).g开发者_如何学PythonetElement('img');

    var delay = 0;  

    for (var keys in banner1array) {
        var callback = (function(key) { return function() {
            banner.setStyle('opacity', 0);
            var object = array[key];
            for (var property in object) {
                if (property == 'href') {
                    var href = object[property];
                }
                if (property == 'src') {
                    var src = object[property];
                }
            }
            if (!banner.getStyle('opacity')) {
                banner.set('tween', {duration:1000});                   
                banner_link.setProperty('href', href);
                banner_image.setProperty('src', src);
                banner.tween('opacity', 1);
            }
        }; })(keys);
        setTimeout(callback, delay);
        delay += 21000;
    }
}

var banner1 = set_banner('banner1', banner1array);
setInterval(function() {set_banner('banner1', banner1array);}, 84000);

var banner2 = set_banner('banner2', banner2array);
setInterval(function() {set_banner('banner2', banner2array);}, 84000);

});

A couple of simple mistake:

 var banner1 = new set_banner('banner1');
               ^ ---------- creates a new object and uses set_banner as the constructor
                            your code already gets called here
                            and you get a new object back, which in this case has NO use

 ....
 setInterval(banner1(), 42000);
                     ^----------------- The parenthesis EXECUTE the function
                                        the RETURN VALUE is then passed to setInterval
                                        BUT... banner1() is NOT a function, so this fails

What you want to do in case that you want to call set_banner after 42 seconds AND pass a parameter is to use an anonymous function which then calls set_banner.

setInterval(function() { // pass an anonymous function, this gets executed after 42 seconds...
    set_banner('banner1'); // ...and then calls set_banner from within itself
}, 42000);

Something else to consider: http://zetafleet.com/blog/why-i-consider-setinterval-harmful. (tl:dr Instead of setInterval, use setTimeout.) While I'm not sure that his arguments apply here, it seems like a good thing to get in the habit of avoiding.

function defer_banner(div, bannerArray, delay) {
  setTimeout(function() {
    setBanner(div, bannerArray);
    defer_banner(div, bannerArray, delay);
  }, delay); 
});