You can't do it that way-- once someone copies the code, it can never be changed by you. What you can change is the contents of the Javascript file. For example

You can't do it that way-- once someone copies the code, it can never be changed by you. What you can change is the contents of the Javascript file. For example, when I make an update to my service, I upload the changes to script.js and the new code is run on the sites that embed that script.