You can use VexFlow in Node JS by calling const Vex = require(...) on the JS library.
node canvas.js > output.html creates an HTML page containing the VexFlow output.
node svg.js > output.svg creates a SVG image file containing the VexFlow output.
node pdf.js produces a PDF file containing the VexFlow output.
node customcontext.js demonstrates how to use VexFlow with a custom RenderContext.
NOTE: The require('vexflow') statement in these demos works because of the vexflow/package.json exports field.