A simple javascript to read the URL

I need a simple javascript on the page that reads the URL parameters to fetch the relevant image. For example: For the URL --> [login to view URL] it takes the value 'abc' and modifies one of the lines on html page as: <img src="[login to view URL]" alt=""> Similarly For --> [login to view URL] it'll write as: <img src="[login to view URL]" alt=""> When no values are passed i.e. for the URL [login to view URL] it'll keep the line as: <img src="[login to view URL]" alt=""> For your reference: [login to view URL] It's a very simple task. Should not take more than 30 minutes (may be less)