boris/node_modules/parent-module/index.js

'use strict';
const callsites = require('callsites');

module.exports = filepath => {
	const stacks = callsites();

	if (!filepath) {
		return stacks[2].getFileName();
	}

	let seenVal = false;

	// Skip the first stack as it's this function
	stacks.shift();

	for (const stack of stacks) {
		const parentFilepath = stack.getFileName();

		if (typeof parentFilepath !== 'string') {
			continue;
		}

		if (parentFilepath === filepath) {
			seenVal = true;
			continue;
		}

		// Skip native modules
		if (parentFilepath === 'module.js') {
			continue;
		}

		if (seenVal && parentFilepath !== filepath) {
			return parentFilepath;
		}
	}
};