Scripts shouldn’t go inside the body of a post, but it is possible for administrator level users.
See the codex info on Javascript_in_Posts.
If you need JS inside a post, chances are you’re approaching it from the wrong angle, content should go in the content area, not code.
However if you’re looking to run code when something specific appears in a post, a better approach(imho) is to use a shortcode(or several), you can read more about them here.