GetServerSideProps: Tell the difference between SSR and client side

[alexanbj]

I was wondering if there is a way to know inside getServerSideProps if it is currently being used used to SSR the page, or if it is being called from the client as an AJAX request.

My particular use case I have quite an expensive operation that I only want to do on the initial SSR. For subsequent calls from the same client I don't want to redo the same operation as it will likely return the same result, so I have cached it on the client.