fix image wrap size with the same size of Lazy Load image

I'm looking for to show background-color image before lazy-loading, with exactly the same dimension of the image. My script get width and height of each images and applises on image-wrap.

my script :

$(document).ready( function(){
    $('section .lazywrap').each(function(){ 

        var lazyWrap = $(this);
        var img = $(lazyWrap, this);

        lazyWrap.width(img.width());
        lazyWrap.height(img.height());

        console.log(lazyWrap.height());
    });
});

my html :

<a href="/" class="lazy-wrap">
  <img class="lazy" width="472" src="img.jpg" data-original="img.jpg" >
</a>

The problem is :

Web browser can get height value even if it's not implemented in <img>, BUT only for images who are visible in the viewport when the page is loading, because of lazy Load.

I read lot of things about responsive background image with the padding-bottom trick, but in my case I really need the real width and height value on this "background preview" and not a ratio. All my image have different height value.

Thanks for your help.