Javascript slideshow issues with getElementById.

[helimeef]

Hiya, I'm upgrading a this slideshow to Object Oriented code (so I can reuse it for other clients), and I'm having some problems getting the library to work. Here is what it's like so far:

(function(){
    var img;
    var imgArr;
    var currSlide = 0;
    function Slideshow(image,slides) {
        img = document.getElementById(image);
        imgArr = slides;
        this.Next=function(amount) {
            if(!amount) var amount=1;
            if(currSlide+1<imgArr.length) {
                currSlide+=amount;
            }
            else {
                currSlide = 0;
            }
            img.src = imgArr[currSlide];
            return this;
        }
        this.Prev = function(amount) {
            if(!amount) var amount=1;
            if(currSlide>0) {
                currSlide-=amount;
            }
            else {
                currSlide = imgArr.length-1;
            }
            img.src = imgArr[currSlide];
            return this;
        }
    }
})();

To create a slideshow and go to the next image (if it worked) you would do this:

var Show = new Slideshow('id_of_image_to_rotate',['img1.png','img2.jpg','img3.gif']);
Show.Next();

However when I do this, HomeSite and FF Error Console tell me "document.getEl emenyById(...) is null or not an object". I have fixed it by wrapping all of the code in window.onload, but what kind of library would require that? I figured that (function() {}); was used to remove that error, but I guess not.
Any ways I can fix this?

[acoder]

Functions are objects, see An Introduction to Function Objects.

[helimeef]

Functions are objects, see An Introduction to Function Objects.

Well, that really wasn't my problem (I think), but I got it to work anyway. I ended up doing this:

var Slideshow;
Slideshow = (function(image_id,slides){
  //the rest...
});
// The code that activates the slideshow
window.onload = function() {
  var show = new Slideshow('image_id',{'1.jpg','2.jpg'});
  show.Next().Previous().Whatever();
}

So I needed to put the code in window.onload. There ya go.