Your code are publicized with your designating license, and others can “fork” it and make his/her branched version.
Here is one Jsdo.it project sample I randomly took. On this blog widget, all source code can be seen on viewer, and you can play it here.
As licenses are attached to each source code by posters, you can take all needed code to your server outside if it permits.
All time favored ranking may be good place to check what cool designs and effects are made by Japanese web programmers.
Kayac, the company behind Jsdo.it, has already succeeded with the similar type of “code and share” community on Adobe Flash, Wonderfl. Some popular Flash applications made on Wonderfl seem to be transplanted to Jsdo.it already.