How do I get the dirname of the calling method when it is in a different file in nodejs?

Use callsite, then:

b.js:

var path = require('path'),
    callsite = require('callsite');

module.exports = {
  someFn: function () {
    var stack = callsite(),
        requester = stack[1].getFileName();

    console.log(path.dirname(requester));
  }
};