An ESnext spec-compliant Object.groupBy shim/polyfill/replacement that works as far down as ES3.
This package implements the es-shim API interface. It works in an ES3-supported environment and complies with the proposed spec.
npm install --save object.groupbyvar groupBy = require('object.groupby'); var assert = require('assert'); var arr = [0, 1, 2, 3, 4, 5]; var parity = function (x) { return x % 2 === 0 ? 'even' : 'odd'; }; var results = groupBy(arr, function (x, i) { assert.equal(x, arr[i]); return parity(x); }); assert.deepEqual(results, { __proto__: null, even: [0, 2, 4], odd: [1, 3, 5], });var groupBy = require('object.groupby'); var assert = require('assert'); /* when Object.groupBy is not present */ delete Object.groupBy; var shimmed = groupBy.shim(); assert.equal(shimmed, groupBy.getPolyfill()); assert.deepEqual(Object.groupBy(arr, parity), groupBy(arr, parity));var groupBy = require('object.groupby'); var assert = require('assert'); /* when Array#group is present */ var shimmed = groupBy.shim(); assert.equal(shimmed, Object.groupBy); assert.deepEqual(Object.groupBy(arr, parity), groupBy(arr, parity));Simply clone the repo, npm install, and run npm test