preloader.js

// http://www.webreference.com/programming/javascript/gr/column3/

function ImagePreloader(images, callback)
{
   // store the callback
   this.callback = callback;
 
   // initialize internal state.
   this.nLoaded = 0;
   this.nProcessed = 0;
   this.aImages = new Array;
 
   // record the number of images.
   this.nImages = images.length;
 
   // for each image, call preload()
   for ( var i = 0; i < images.length; i++ )
      this.preload(images[i]);
}

ImagePreloader.prototype.preload = function(image)
{
   // create new Image object and add to array
   var oImage = new Image;
   this.aImages.push(oImage);
  
   // set up event handlers for the Image object
   oImage.onload = ImagePreloader.prototype.onload;
   oImage.onerror = ImagePreloader.prototype.onerror;
   oImage.onabort = ImagePreloader.prototype.onabort;
  
   // assign pointer back to this.
   oImage.oImagePreloader = this;
   oImage.bLoaded = false;
  
   // assign the .src property of the Image object
   oImage.src = image;
}

ImagePreloader.prototype.onComplete = function()
{
   this.nProcessed++;
   if ( this.nProcessed == this.nImages )
   {
      this.callback(this.aImages, this.nLoaded);
   }
}

ImagePreloader.prototype.onload = function()
{
   this.bLoaded = true;
   this.oImagePreloader.nLoaded++;
   this.oImagePreloader.onComplete();
}

ImagePreloader.prototype.onerror = function()
{
   this.bError = true;
   this.oImagePreloader.onComplete();
}

ImagePreloader.prototype.onabort = function()
{
   this.bAbort = true;
   this.oImagePreloader.onComplete();
}