client responsive image url

@responsiveImageUrl = (image_path) ->
    if window.devicePixelRatio > 1
        isRetina = true
    else
        isRetina = false

    width = $(window).width()
    height = $(window).height()
    url = '/rimage/?image_path=' + image_path + '&width=' + width + '&height=' + height
    if isRetina
        url += '&is_retina=' + isRetina
    return url

url = responsiveImageUrl('STATIC_URL+'img/img1.png')