imagesPreloader.js

directive('preload-css-images', function () {
    var image_regexp = /url\(['"]?\S*['"]?\)/;
    for (var i = 0; i < document.styleSheets.length; i++) {
        var styleSheet = document.styleSheets[i];
        var rules = styleSheet.cssRules || styleSheet.rules;
        if (rules && rules.length)
            for (var j = 0; j < rules.length; j++) {
                var image_urls = image_regexp.exec(rules[j].cssText);
                if (image_urls) for (var k = 0; k < image_urls.length; k++) {
                    document.createElement('img').src = image_urls[k]
                        .replace('url(', '')
                        .replace(')', '')
                        .split('"').join('')
                        .split("'").join('');
                }
            }
    }
});