Available in all subroutines.
Returns the given URL but only keeps the listed parameters.
set req.url = querystring.filter(req.url, "q" + querystring.filtersep() + "p");
Try it out
querystring.filter_except is used in the following solution recipes, which show real world use cases. Click RUN to provision a Fastly service, execute the code on Fastly, and see how the function behaves.
Improve cache performance by normalizing requests. Filter and reorder query params, convert to lowercase, filter headers, and more.
Image transformation classes
Use custom, predefined classnames like large, medium, small, teaser, thumb, or article to control Fastly Image Optimizer and optionally prevent end-user access to native properties like 'width'.
User contributed notes
We welcome comments that add use cases, ideas, tips, and caveats. All comments will be moderated before publication. To post support questions, visit our support center and we'll find you the help you need.