How do I check if a url contains a QueryString?

Hi,
The first time the user navigates to my page there will be no query string in the url.
The page will display them 10 posts, and at the bottom there will be a 'next page' button that will call the same page but this time pass the page a pageNumber in a query string and the next ten posts will be displayed.
how can I detect if there is a QueryString in the url so that only when the page is called by the 'next page' button and there is a QueryString is my code exicuted?
 
Thanks. 
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