预加载 Jquery 悬停图像

Question

Right now I am building a map of the US, and when you hover over any given state, I am replacing the image with an image of a different color.

My problem is that the way I am currently doing things, the image is being replaced and a new image loaded on hover.

I have the HTML laid out as:

<img class="state" id="alaska" src="img/united-states_Alaska.png" alt="alaska">
<img class="state" id="hawaii" src="img/united-states_hawaii.png" alt="hawaii">

And the jQuery I am using is:

$('.interactive-map img').each(function(e){
    var src = $(this).attr('src');
    $(this).hover(function(){
      $(this).attr('src', src.replace('.png', '-hover.png'));
    }, function(){
      $(this).attr('src', src);
    });
});

I am curious if there is another way to either preload the images with JavaScript, or make it so that there isn't a new request for image every time I hover. I would like to not have to change the HTML or CSS much and optimize it in JavaScript.

Answer 1

Add your images to the DOM on page load but in hidden state, then they get cached

$(function() {
 var images = ['url/to/your/jpg1.jpg', 'ur/to/your/png2.png'];
 var d = document.createElement("div");
 d.style.display = 'none';
 document.body.appendChild(d);
 for (var i in images) 
 {
   var img = document.createElement("img");
   img.src = images[i];
   d.appendChild(img);
 }
});

Answer 2

Have two image tags and set the first image's display: block . Set the second image's display: none .

Then on hover you switch the them. It is as easy as that.

Answer 3

Use PreloadJS

Example:

var preload = new createjs.LoadQueue();
preload.addEventListener("fileload", handleFileComplete);
preload.loadFile('http://createjs.com/images/404/gBot-confused.jpg');
function handleFileComplete(event) {
    document.body.appendChild(event.result);
}

Full Docs: here

Another interesting post using JS and AJAX: Preloading