如何给图片做缓存

 1 function preloadImages(array) {
 2     if (!preloadImages.list) {
 3         preloadImages.list = [];
 4     }
 5     for (var i = 0; i < array.length; i++) {
 6         var img = new Image();
 7         img.onload = function() {
 8             var index = preloadImages.list.indexOf(this);
 9             if (index !== -1) {
10                 // remove this one from the array once it‘s loaded
11                 // for memory consumption reasons
12                 preloadImages.splice(index, 1);
13             }
14         }
15         preloadImages.list.push(img);
16         img.src = array[i];
17     }
18 }
19 
20 preloadImages(["url1.jpg", "url2.jpg", "url3.jpg"]);