Scala expression to replace a file extension in a string

Question

Here is a version I wrote using split:

fileName.split('.').init ++ Seq("js") mkString "."

This transforms e.g. foo.bar.coffee into foo.bar.js.

What I like:

• it works
• it doesn't rely on things like indexOf()
• it feels functional ;)

What I don't like:

• it's not as short as I would hope
• it might confuse some readers

How can I write an even simpler / straightforward version?

UPDATE: Great answers below! In short:

• seems like my original approach above was not bad although it doesn't cover some corner cases, but that's fixable with a longer expression if you need to cover those
• another, slightly shorter approach uses regexps, which will be more or less readable depending on your regexp background

• a slightly shorter syntax for the original approach (corner cases not covered) reads:

  fileName.split('.').init :+ "js" mkString "."

Answer 1

If you know what the current extension is, then you could do this:

def replaceExtension(fileName: String, oldExt: String, newExt: String): String =
  fileName.stripSuffix(oldExt) + newExt

// Be sure to use `.` when calling:
replaceExtension(fileName, ".javascript", ".js")