JQuery: Check if image is in browser cache

gistfile1

alert("Expected: true or false\n" +
cached(big_img)
+ "\n\nExpected: false (cache-busting enabled)\n" +
cached(big_img + "?" + new Date().getTime()));

function cached(url){
    var test = document.createElement("img");
    test.src = url;
    return test.complete || test.width+test.height > 0;
}