Hook into backbone to add js to wp-admin -> media library?

You can enqueue javascript files and css files like this for wp admin:-

    function load_custom_wp_admin_style() {
        wp_enqueue_script( 'script-name','js/scripts.js', array('jquery'), '3.3.5', true );
}
add_action( 'admin_enqueue_scripts', 'load_custom_wp_admin_style' );

First you need to enqueue admin scripts like below:-

 function my_admin_scripts() {
wp_enqueue_script('media-upload');
wp_enqueue_script('thickbox');
}

function my_admin_styles() {
wp_enqueue_style('thickbox');
}

for uploading attachment:-

 $('.upload_image_button').live('click',function() {
         formfield = $('#upload_image').attr('name');
         tb_show('', 'media-upload.php?type=image&TB_iframe=true');
         return false;
        });

         window.send_to_editor = function(html) {
         imgurl = $('img',html).attr('src');
         tb_remove();
        }

I have used my code, you can modify it.

Thanks