Maybe because Jupyter has already more than 70 kernels and got adopted before other notebooks appeared (Beaker, Spark, Zeppelin)?
there are lot more differences in the UI as well.
The %Rpush and %Rpull magics are what you need.
Also, if you are using Spark, then Apache Toree[1] lets you use Python, R, Scala and SQL in the same notebook against Spark[2].
[1] https://toree.incubator.apache.org/documentation/user/how-it...
[2] https://github.com/ibm-et/spark-kernel/wiki/Language-Support...
here are some examples of JS working in beaker (in addition to the above python/JS demo):
https://pub.beakernotebook.com/publications/87a444cc-fb85-11...
https://pub.beakernotebook.com/publications/797f99f2-fccd-11...
https://pub.beakernotebook.com/publications/afa0f71c-4aaf-11...