This library is just a convenient container of as many EPSG definitions of possible. For when "just make it work" is more important than saving bytes.
Note: epsg-index is probably a better alternative in most cases.
Usage:
var epsg = require('epsg')
console.log(epsg['EPSG:3857']);
// +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs
You can access the crs-defs.json file directly if that's useful, for instance with the reproject library:
reproject --crs-defs=node_modules/epsg/crs-defs.json ...