Problem setting up developer environment for vextab project

[Blues for Greeny]

I am very interested in exploring Vextab for some development work. I am having a problem getting past the tests however. Can anyone help?

I cloned the vextab repository on my linux machine and followed the Developer instructions in the Readme doc. When I run the tests I see several of the same warnings:

Warning:  Unsorted keys in note will be sorted. See https://github.com/0xfe/vexflow/issues/104 for details. undefined

And the the following error: 

Message: Died on test #2 Start@file:///~/vextab/build/vextab-tests.js:58185:9: undefined is not a function (near '...$position)[position]();...')

I also tried the ../tests/vextab-standalone.html page and see this error:

((((intermediate value)(intermediate value) , _defineProperty(...)) , _defineProperty(...)) , _ABOVE$BELOW$position)[position] is not a function

I traced this down to the vextab line:

notes :8 (12/5.12/4)ds(5/5.5/4)u 3b4/5

where the build code does not like the use of the Up/Down specification.

$ node -v

v5.5.0

$ npm -v

3.3.12

[Kenny Salter]

I had a similar problem setting up my dev environment for the whole vexflow.js library. I used the cdn link to bring vexflow into my project rather than npm because when I did use npm install vexflow it installed successfully but my code kept getting this error "vex not defined". I still haven't figured out why this is happening with the npm install but using the cdn link worked correctly for me.