JavaScript controls the method of calling the callback function after the image is loaded_javascript skills

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_cntr = 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_cntr ;
If (img_load_cntr == img_length) {
                 callback();
            }
        });
}
else { //otherwise just do the main callback action if there's no images in $img_container.
        callback();
}
}