fetch media attachments via javascript in wp

fetch attachment

for(i=0;i<selected_ids.length;i++){
    if(selected_ids[i]>0){
        var attachment = new wp.media.model.Attachment.get(selected_ids[i]);
        attachment.fetch({success:function(att){
            container.append("<li><img src='" + att.attributes.sizes.thumbnail.url + "'</li>");
        }});
    }
}