You can add a custom control on your master pages or pages that will add the js code you want. Another option is using Generic Content control.
It would not be possible to add js code without editing a master page( template) or a page.
You can add some code to all pages if you inherit from the base page class - InternalPage, but this depends on results you want to have.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items