Unable to launch vega-editor

The vega-editor allows interactive editing and viewing of rendered vega and vega-lite visualizations. https://github.com/vega/vega-editor

I have installed it according to the directions on the README.md. The npm link did not work in either vega or vega-lite: so I manually copied the .js into the vega-editor/vendor directory:

 $pwd
/git/vega-editor/vendor
05:51:58/vendor $ll vega*.js
-rw-r--r--  1 boescst  admin  405255 Apr 30 23:49 vega-lite.js
-rw-r--r--  1 boescst  admin  170943 Apr 30 23:50 vega-lite.min.js
-rw-r--r--  1 boescst  admin  879846 May 14 00:29 vega.js
-rw-r--r--  1 boescst  admin  553130 May 14 00:29 vega-core.js
-rw-r--r--  1 boescst  admin  386015 May 14 00:29 vega.min.js
-rw-r--r--  1 boescst  admin  234204 May 14 00:29 vega-core.min.js
-rw-r--r--  1 boescst  admin   17694 May 14 05:31 vega-embed.min.js
-rw-r--r--  1 boescst  admin   93163 May 14 05:31 vega-embed.js

That did fix the 404 issues with the vega.js and vega-lite.js . The main index.html only shows blank page however. Using view source we see:

So what might be missing here to get the editor web page up?

via javadba