imageurl = "/images/products/" + item.id + "/" + item.productimage
$.ajax({
    url: imageurl,
    type: 'HEAD',
    error: function() {
        //file not exists
        imageurl = "/images/products/" + item.productimage
    },
    success: function() {
        //file exists
        imageurl = "/images/products/" + item.id + "/" + item.productimage
    }
});
console.log('image: ' + imageurl);