Detect whether a page is a product subcategory page?

How can I detect whether current page is a product sub category page?

I’ve tried with the following but it will always print out “NO”

function is_subcategory($category = null) {
    if (is_category()) {
        if (null != $category){
            $cat = get_category($category);
        }else{
            $cat = get_category(get_query_var('cat'),false);
        }
        if ($cat->parent == 0 ){
            return false;
        }else{
            return true;
        }
    }
    return false;
}

if (is_subcategory()){
    echo "YES";
}else{
    echo "NO";
}

is_category() only check the built in post category. Product categories are custom taxonomies. So you need to use is_tax() instead of is_category() and get_term() instead of get_category().

Check this example:-

function is_subcategory($cat_id = null) {
    if (is_tax('product_cat')) {

        if (empty($cat_id)){
            $cat_id = get_queried_object_id();
        }

        $cat = get_term(get_queried_object_id(), 'product_cat');
        if ( empty($cat->parent) ){
            return false;
        }else{
            return true;
        }
    }
    return false;
}

Also safe side instead of get_query_var() use get_queried_object_id()