This package cannot be used for OSX. It is tested for Windows and Linux.
npm install nodeaffinity
var nc = require('nodeaffinity');
//Returns the cpus/cores (affinity mask) on which current node process is allowed to run
//Failure returns -1
console.log(nc.getAffinity());
//Sets process CPU affinity, here 3 means 011 i.e. process will be allowed to run on cpu0 and cpu1
// returns same mask id success , if failure retuen -1.
console.log(nc.setAffinity(3));