Make JavaScript in any editor you have handy. Open a web browser and run it.
I'm astounded that people continually whinge about the alleged lack of a programming environment on modern computers. Even Windows 7, which is not especially developer friendly when installed by a typical vendor, has a programming environment that has capabilities wildly beyond anything available on a machine from fifteen years ago.
While you can download Visual Studio Express or simply install the optional XCode package, depending on your platform, the humble web browser is actually capable of an awful lot all by itself.
I have to strongly disagree that older BASIC-prompt type computers were "a million times easier to program". Ask anyone who's had to debug a 500 line BASIC program without a proper editor how "easy" it is. Notepad, while not an IDE, is a vast improvement over line-by-line entry.
Although opening a browser and running a few JavaScript commands is not as intuitive as the old 10 PRINT "HELLO", 20 GOTO 10, the poisonously bad habits of BASIC shouldn't be taught anyway.
Consider a simple test-case:
What is the most impressive thing that someone unfamiliar with computers can manage within 72 hours of unboxing?
On a C64-vintage machine the answer is quite likely some kind of BASIC "What is your name?" type program that produces a variety of witty answers, or where someone has a better reference, a sprite that bounces around off the edges of the screen.
On a modern machine with a browser, it could be a web page for a school project, a video on YouTube, or a small game built using some of the web-based frameworks.
Embedding a YouTube video in a forum post might not be "programming" in the strictest sense, but I'd argue that getting the computer to do what you want is the important thing, and only sometimes conventional programming is required.