The idea of lively code comes from Dan Ingalls, a developer of Smalltalk. In Scratch 1.x, as in Snap!, it's provided by Morphic. The version of Morphic used in Scratch, written in Smalltalk, was developed by John Maloney. Snap! 's Morphic, of course, was written in Javascript by Jens. I'm not on top of the history of more recent versions of Scratch.
Scratch 2.0 was written in flash, but I'm not entirely sure how they achieved lively code. Scratch 3.0 uses google's blockely, which I'm assuming allows for lively code, although scratch did heavily modify blockely so that they could get the scratch block shape, and all the stuff that was in the previous versions. I just know that there is a scratch vm that is what runs the code.
i dont even think node was a thing or was in development when morphic.js was released