Question

I have created a simple photo gallery viewer, and I would like to preload the images in the background, and then run a function when they are done.

My question is, how do I do that?

Answer 1

var image = new Image();
image.src = "http://foo.com/myimage.jpg";

//if you have a div on the page that's waiting for this image...
var div = getElementById("imageWrapperDiv");

//you can set it on the image object as the item to draw into...
image.myDiv = div;

image.onload = function(){
  //do whatever you're going to do to display the image

  //so in this example, because I have set this objects myDiv property to a div on the page
 // I can then just populate that div with an img tag.
 //it's not the most elegant solution, but you get the idea and can improve upon it easily
  this.myDiv.innerHTML = "<img src='" +  this.src  +"'>";
}

Once the image loads, it’s in the browser’s cache, so, if you use the src property you can draw it anywhere on the page and it will display instantly.