findDupes.js

const fs = require('fs');
const path = require('path');
const { uniq, groupBy, pickBy } = require('lodash');

const beautifiedJsFile = fs.readFileSync(path.join(__dirname, './build.js'), 'utf-8');

const nodeModulesRegex = /"(.*?\/node_modules\/.*?)"/;

const findNodeModules = ( str ) => {
  const lines = str.split('\n');
  const modules = [];
  lines.forEach(line => {
    if (line.includes(`/node_modules/`)) {
      const match = line.match(nodeModulesRegex);
      modules.push(match[1]);
    }
  })

  return uniq(modules);
};

const getRealModuleName = ( str ) => {
  return str.substr(str.lastIndexOf('/node_modules/'));
};


const findDupes = ( str ) => {
  const modules = findNodeModules(str);
  return pickBy(
    groupBy(modules, getRealModuleName),
    ( val, key ) => val.length > 1
  );
};

console.log(findDupes(beautifiedJsFile));