title: How can I test JavaScript without placing it on the website?
body: <p>I'm talking about something like GreaseMonkey but that would accept the script just as it would be on the website. Adding external scripts to Greasemonkey has been a pain for me so far.</p>
  
  <p>So, I have a client who wanted me to write a specific script for him. Because the script reads the URL of the page visited by a user I can only test it on the website but i don't have access to the source code of the website. I'd like to make sure I deliver to the client a 100% working script so I would love to test it first. </p>
  
  <p>How can I do that? Any plugins that would just allow me to copy the script and would run it every time I load a page of the website?</p>