Elevation data for your GeoJSON as a micro service. Yes, really!
You can try it out in the elevation-service demo app.
You might also be interested in geojson-elevation and node-hgt, which this module builds upon.
Clone this repo, install dependencies:
npm install
and fire it up:
npm start
It runs on port 3000 for now.
Post a GeoJSON object to its only endpoint, /, and you will get the same object back, but its
coordinates will have a third component containing elevation added.