JavaScript控制图片加载完成后调用回调函数的方法

function when_images_loaded($img_container, callback) {
/ do callback when images in $img_container (jQuery object) are loaded. Only works when ALL images in $img_container are newly inserted images and this function is called immediately after images are inserted into the target. /
    var _imgs = $img_container.find('img'),
        img_length = _imgs.length,
        img_load_tr = 0;
    if (img_length) {//if the $img_container contains new images.
        _imgs.on('load', function() {//then we avoid the callback until images are loaded
            img_load_tr++;
            if (img_load_tr == img_length) {
                callback();
            }
        });
    }
    else { //otherwise just do the main callback action if there's no images in $img_container.
        callback();
    }
}