diff --git a/.gitignore b/.gitignore
index 9fad026..35e6d38 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,4 @@
 node_modules/
-lib/
 .DS_Store
 npm-debug.log
 package-lock.json
diff --git a/.npmignore b/.npmignore
index 4ac9f03..3a93ddb 100644
--- a/.npmignore
+++ b/.npmignore
@@ -4,5 +4,4 @@ script/
 .DS_Store
 npm-debug.log
 .travis.yml
-dist/
 bower.json
diff --git a/babel.config.js b/babel.config.js
deleted file mode 100644
index 0d779b8..0000000
--- a/babel.config.js
+++ /dev/null
@@ -1,20 +0,0 @@
-let presets = [];
-
-let plugins = [
-  ["@babel/plugin-proposal-optional-chaining", { loose: false }],
-  ["@babel/plugin-proposal-nullish-coalescing-operator", { loose: false }],
-];
-
-if (process.env.BABEL_ENV === "development") {
-  plugins.push(...[
-    "@babel/plugin-transform-modules-commonjs",
-    "@babel/plugin-proposal-export-namespace-from",
-  ]);
-}
-
-module.exports = {
-  presets: presets,
-  plugins: plugins,
-  exclude: "node_modules/**",
-  sourceMap: true,
-};
diff --git a/bower.json b/bower.json
deleted file mode 100644
index 484a2f4..0000000
--- a/bower.json
+++ /dev/null
@@ -1,29 +0,0 @@
-{
-  "name": "underscore-plus",
-  "homepage": "https://github.com/atom/underscore-plus",
-  "authors": [
-    "Kevin Sawicki <kevinsawicki@gmail.com>",
-    "Matt Colyer <matt@colyer.name>",
-    "benogle <ogle.ben@gmail.com>",
-    "nathansobo <nathan@github.com>"
-  ],
-  "description": "Underscore with some extensions",
-  "main": "./dist/underscore-plus.js",
-  "keywords": [
-    "underscore"
-  ],
-  "license": "MIT",
-  "ignore": [
-    "**/.*",
-    "node_modules",
-    "bower_components",
-    "spec",
-    "src",
-    "lib",
-    "Gruntfile.coffee",
-    "package.json"
-  ],
-  "dependencies": {
-    "underscore": "1.x"
-  }
-}
diff --git a/dist/underscore-plus.js b/dist/underscore-plus.js
deleted file mode 100644
index 5f0a7a5..0000000
--- a/dist/underscore-plus.js
+++ /dev/null
@@ -1,647 +0,0 @@
-"use strict";
-
-Object.defineProperty(exports, "__esModule", {
-  value: true
-});
-var _exportNames = {
-  adviseBefore: true,
-  camelize: true,
-  capitalize: true,
-  compactObject: true,
-  dasherize: true,
-  deepClone: true,
-  deepExtend: true,
-  deepContains: true,
-  endsWith: true,
-  escapeAttribute: true,
-  escapeRegExp: true,
-  humanizeEventName: true,
-  humanizeKey: true,
-  humanizeKeystroke: true,
-  isSubset: true,
-  losslessInvert: true,
-  mapObject: true,
-  multiplyString: true,
-  pluralize: true,
-  remove: true,
-  setValueForKeyPath: true,
-  hasKeyPath: true,
-  spliceWithArray: true,
-  sum: true,
-  uncamelcase: true,
-  undasherize: true,
-  underscore: true,
-  valueForKeyPath: true,
-  isEqual: true,
-  isEqualForProperties: true
-};
-exports.adviseBefore = adviseBefore;
-exports.camelize = camelize;
-exports.capitalize = capitalize;
-exports.compactObject = compactObject;
-exports.dasherize = dasherize;
-exports.deepClone = deepClone;
-exports.deepExtend = deepExtend;
-exports.deepContains = deepContains;
-exports.endsWith = endsWith;
-exports.escapeAttribute = escapeAttribute;
-exports.escapeRegExp = escapeRegExp;
-exports.humanizeEventName = humanizeEventName;
-exports.humanizeKey = humanizeKey;
-exports.humanizeKeystroke = humanizeKeystroke;
-exports.isSubset = isSubset;
-exports.losslessInvert = losslessInvert;
-exports.mapObject = mapObject;
-exports.multiplyString = multiplyString;
-exports.pluralize = pluralize;
-exports.remove = remove;
-exports.setValueForKeyPath = setValueForKeyPath;
-exports.hasKeyPath = hasKeyPath;
-exports.spliceWithArray = spliceWithArray;
-exports.sum = sum;
-exports.uncamelcase = uncamelcase;
-exports.undasherize = undasherize;
-exports.underscore = underscore;
-exports.valueForKeyPath = valueForKeyPath;
-exports.isEqual = isEqual;
-exports.isEqualForProperties = isEqualForProperties;
-
-var _underscore = require("underscore");
-
-Object.keys(_underscore).forEach(function (key) {
-  if (key === "default" || key === "__esModule") return;
-  if (Object.prototype.hasOwnProperty.call(_exportNames, key)) return;
-  Object.defineProperty(exports, key, {
-    enumerable: true,
-    get: function () {
-      return _underscore[key];
-    }
-  });
-});
-// import * as _ from 'underscore' // if we needed all
-const macModifierKeyMap = {
-  cmd: '\u2318',
-  ctrl: '\u2303',
-  alt: '\u2325',
-  option: '\u2325',
-  shift: '\u21e7',
-  enter: '\u23ce',
-  left: '\u2190',
-  right: '\u2192',
-  up: '\u2191',
-  down: '\u2193',
-  cmdorctrl: '\u2318'
-};
-const nonMacModifierKeyMap = {
-  cmd: 'Cmd',
-  ctrl: 'Ctrl',
-  alt: 'Alt',
-  option: 'Alt',
-  shift: 'Shift',
-  enter: 'Enter',
-  left: 'Left',
-  right: 'Right',
-  up: 'Up',
-  down: 'Down',
-  cmdorctrl: 'Ctrl'
-}; // Human key combos should always explicitly state the shift key. This map is a disambiguator.
-// 'shift-version': 'no-shift-version'
-
-const shiftKeyMap = {
-  '~': '`',
-  '_': '-',
-  '+': '=',
-  '|': '\\',
-  '{': '[',
-  '}': ']',
-  ':': ';',
-  '"': '\'',
-  '<': ',',
-  '>': '.',
-  '?': '/'
-};
-
-function splitKeyPath(keyPath) {
-  let startIndex = 0;
-  const keyPathArray = [];
-
-  if (keyPath == null) {
-    return keyPathArray;
-  }
-
-  for (let i = 0; i < keyPath.length; i++) {
-    const char = keyPath[i];
-
-    if (char === '.' && (i === 0 || keyPath[i - 1] !== '\\')) {
-      keyPathArray.push(keyPath.substring(startIndex, i));
-      startIndex = i + 1;
-    }
-  }
-
-  keyPathArray.push(keyPath.substr(startIndex, keyPath.length));
-  return keyPathArray;
-}
-
-const isPlainObject = value => (0, _underscore.isObject)(value) && !(0, _underscore.isArray)(value);
-
-function adviseBefore(object, methodName, advice) {
-  const original = object[methodName];
-  return object[methodName] = function (...args) {
-    if (advice.apply(this, args) !== false) {
-      return original.apply(this, args);
-    }
-  };
-}
-
-function camelize(string) {
-  if (string) {
-    return string.replace(/[_-]+(\w)/g, m => m[1].toUpperCase());
-  } else {
-    return '';
-  }
-}
-
-function capitalize(word) {
-  if (!word) {
-    return '';
-  }
-
-  if (word.toLowerCase() === 'github') {
-    return 'GitHub';
-  } else {
-    return word[0].toUpperCase() + word.slice(1);
-  }
-}
-
-function compactObject(object) {
-  const newObject = {};
-
-  for (let key in object) {
-    const value = object[key];
-
-    if (value != null) {
-      newObject[key] = value;
-    }
-  }
-
-  return newObject;
-}
-
-function dasherize(string) {
-  if (!string) {
-    return '';
-  }
-
-  string = string[0].toLowerCase() + string.slice(1);
-  return string.replace(/([A-Z])|(_)/g, function (m, letter) {
-    if (letter) {
-      return "-" + letter.toLowerCase();
-    } else {
-      return "-";
-    }
-  });
-} // Deep clones the given JSON object.
-//
-// `object` - The JSON object to clone.
-//
-// Returns a deep clone of the JSON object.
-
-
-function deepClone(object) {
-  if ((0, _underscore.isArray)(object)) {
-    return object.map(value => deepClone(value));
-  } else if ((0, _underscore.isObject)(object) && !(0, _underscore.isFunction)(object)) {
-    return mapObject(object, (key, value) => [key, deepClone(value)]);
-  } else {
-    return object;
-  }
-}
-
-function deepExtend(target) {
-  let result = target;
-  let i = 0;
-
-  while (++i < arguments.length) {
-    const object = arguments[i];
-
-    if (isPlainObject(result) && isPlainObject(object)) {
-      const keys = Object.keys(object);
-
-      for (let key of keys) {
-        result[key] = deepExtend(result[key], object[key]);
-      }
-    } else {
-      result = deepClone(object);
-    }
-  }
-
-  return result;
-}
-
-function deepContains(array, target) {
-  if (array == null) {
-    return false;
-  }
-
-  for (let object of array) {
-    if ((0, _underscore.isEqual)(object, target)) {
-      return true;
-    }
-  }
-
-  return false;
-}
-
-function endsWith(string, suffix) {
-  if (suffix == null) {
-    suffix = '';
-  }
-
-  if (string) {
-    return string.indexOf(suffix, string.length - suffix.length) !== -1;
-  } else {
-    return false;
-  }
-}
-
-function escapeAttribute(string) {
-  if (string) {
-    return string.replace(/"/g, '&quot;').replace(/\n/g, '').replace(/\\/g, '-');
-  } else {
-    return '';
-  }
-}
-
-function escapeRegExp(string) {
-  if (string) {
-    return string.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&');
-  } else {
-    return '';
-  }
-}
-
-function humanizeEventName(eventName, eventDoc) {
-  const [namespace, event] = eventName.split(':');
-
-  if (event == null) {
-    return undasherize(namespace);
-  }
-
-  const namespaceDoc = undasherize(namespace);
-
-  if (eventDoc == null) {
-    eventDoc = undasherize(event);
-  }
-
-  return `${namespaceDoc}: ${eventDoc}`;
-}
-
-function humanizeKey(key, platform = process.platform) {
-  if (!key) {
-    return key;
-  }
-
-  const modifierKeyMap = platform === 'darwin' ? macModifierKeyMap : nonMacModifierKeyMap;
-
-  if (modifierKeyMap[key]) {
-    return modifierKeyMap[key];
-  } else if (key.length === 1 && shiftKeyMap[key] != null) {
-    return [modifierKeyMap.shift, shiftKeyMap[key]];
-  } else if (key.length === 1 && key === key.toUpperCase() && key.toUpperCase() !== key.toLowerCase()) {
-    return [modifierKeyMap.shift, key.toUpperCase()];
-  } else if (key.length === 1 || /f[0-9]{1,2}/.test(key)) {
-    return key.toUpperCase();
-  } else {
-    if (platform === 'darwin') {
-      return key;
-    } else {
-      return capitalize(key);
-    }
-  }
-} // Humanize the keystroke according to platform conventions. This method
-// attempts to mirror the text the given keystroke would have if displayed in
-// a system menu.
-//
-// keystroke - A String keystroke to humanize such as `ctrl-O`.
-// platform  - An optional String platform to humanize for (default:
-//             `process.platform`).
-//
-// Returns a humanized representation of the keystroke.
-
-
-function humanizeKeystroke(keystroke, platform = process.platform) {
-  if (!keystroke) {
-    return keystroke;
-  }
-
-  const keystrokes = keystroke.split(' ');
-  const humanizedKeystrokes = [];
-
-  for (keystroke of keystrokes) {
-    let keys = [];
-    const splitKeystroke = keystroke.split('-');
-
-    for (let index = 0; index < splitKeystroke.length; index++) {
-      // Check for consecutive dashes such as cmd--
-      let key = splitKeystroke[index];
-
-      if (key === '' && splitKeystroke[index - 1] === '') {
-        key = '-';
-      }
-
-      if (key) {
-        keys.push(humanizeKey(key, platform));
-      }
-    }
-
-    keys = (0, _underscore.uniq)((0, _underscore.flatten)(keys));
-
-    if (platform === 'darwin') {
-      keys = keys.join('');
-    } else {
-      keys = keys.join('+');
-    }
-
-    humanizedKeystrokes.push(keys);
-  }
-
-  return humanizedKeystrokes.join(' ');
-}
-
-function isSubset(potentialSubset, potentialSuperset) {
-  return (0, _underscore.every)(potentialSubset, element => (0, _underscore.include)(potentialSuperset, element));
-}
-
-function losslessInvert(hash) {
-  const inverted = {};
-
-  for (let key in hash) {
-    const value = hash[key];
-
-    if (inverted[value] == null) {
-      inverted[value] = [];
-    }
-
-    inverted[value].push(key);
-  }
-
-  return inverted;
-} // Transform the given object into another object.
-//
-// `object` - The object to transform.
-// `iterator` -
-//   A function that takes `(key, value)` arguments and returns a
-//   `[key, value]` tuple.
-//
-// Returns a new object based with the key/values returned by the iterator.
-
-
-function mapObject(object, iterator) {
-  const newObject = {};
-  const keys = Object.keys(object);
-
-  for (let key of keys) {
-    let value;
-    [key, value] = iterator(key, object[key]);
-    newObject[key] = value;
-  }
-
-  return newObject;
-}
-
-function multiplyString(string, n) {
-  let finalString = "";
-  let i = 0;
-
-  while (i < n) {
-    finalString += string;
-    i++;
-  }
-
-  return finalString;
-}
-
-function pluralize(count = 0, singular, plural = singular + 's') {
-  if (count === 1) {
-    return `${count} ${singular}`;
-  } else {
-    return `${count} ${plural}`;
-  }
-}
-
-function remove(array, element) {
-  const index = array.indexOf(element);
-
-  if (index >= 0) {
-    array.splice(index, 1);
-  }
-
-  return array;
-}
-
-function setValueForKeyPath(object, keyPath, value) {
-  const keys = splitKeyPath(keyPath);
-
-  while (keys.length > 1) {
-    const key = keys.shift();
-
-    if (object[key] == null) {
-      object[key] = {};
-    }
-
-    object = object[key];
-  }
-
-  if (value != null) {
-    object[keys.shift()] = value;
-  } else {
-    delete object[keys.shift()];
-  }
-}
-
-function hasKeyPath(object, keyPath) {
-  const keys = splitKeyPath(keyPath);
-
-  for (let key of keys) {
-    if (!object.hasOwnProperty(key)) {
-      return false;
-    }
-
-    object = object[key];
-  }
-
-  return true;
-}
-
-function spliceWithArray(originalArray, start, length, insertedArray, chunkSize = 100000) {
-  if (insertedArray.length < chunkSize) {
-    originalArray.splice(start, length, ...insertedArray);
-  } else {
-    originalArray.splice(start, length);
-
-    for (let chunkStart = 0, end = insertedArray.length; chunkStart <= end; chunkStart += chunkSize) {
-      originalArray.splice(start + chunkStart, 0, ...insertedArray.slice(chunkStart, chunkStart + chunkSize));
-    }
-  }
-}
-
-function sum(array) {
-  let sum = 0;
-
-  for (let elt of array) {
-    sum += elt;
-  }
-
-  return sum;
-}
-
-function uncamelcase(string) {
-  if (!string) {
-    return '';
-  }
-
-  const result = string.replace(/([A-Z])|_+/g, (match, letter = '') => ` ${letter}`);
-  return capitalize(result.trim());
-}
-
-function undasherize(string) {
-  if (string) {
-    return string.split('-').map(capitalize).join(' ');
-  } else {
-    return '';
-  }
-}
-
-function underscore(string) {
-  if (!string) {
-    return '';
-  }
-
-  string = string[0].toLowerCase() + string.slice(1);
-  return string.replace(/([A-Z])|-+/g, (match, letter = '') => `_${letter.toLowerCase()}`);
-}
-
-function valueForKeyPath(object, keyPath) {
-  const keys = splitKeyPath(keyPath);
-
-  for (let key of keys) {
-    object = object[key];
-
-    if (object == null) {
-      return;
-    }
-  }
-
-  return object;
-}
-
-function isEqual(a, b, aStack, bStack) {
-  if ((0, _underscore.isArray)(aStack) && (0, _underscore.isArray)(bStack)) {
-    return isEqual_(a, b, aStack, bStack);
-  } else {
-    return isEqual_(a, b);
-  }
-}
-
-function isEqualForProperties(a, b, ...properties) {
-  // TODO is Array.from needed?
-  for (let property of Array.from(properties)) {
-    if (!(0, _underscore.isEqual)(a[property], b[property])) {
-      return false;
-    }
-  }
-
-  return true;
-}
-
-function isEqual_(a, b, aStack = [], bStack = []) {
-  if (a === b) {
-    return (0, _underscore.isEqual)(a, b);
-  }
-
-  if ((0, _underscore.isFunction)(a) || (0, _underscore.isFunction)(b)) {
-    return (0, _underscore.isEqual)(a, b);
-  }
-
-  let stackIndex = aStack.length;
-
-  while (stackIndex--) {
-    if (aStack[stackIndex] === a) {
-      return bStack[stackIndex] === b;
-    }
-  }
-
-  aStack.push(a);
-  bStack.push(b);
-  let equal = false;
-
-  if ((0, _underscore.isFunction)(a === null || a === void 0 ? void 0 : a.isEqual)) {
-    equal = a.isEqual(b, aStack, bStack);
-  } else if ((0, _underscore.isFunction)(b === null || b === void 0 ? void 0 : b.isEqual)) {
-    equal = b.isEqual(a, bStack, aStack);
-  } else if ((0, _underscore.isArray)(a) && (0, _underscore.isArray)(b) && a.length === b.length) {
-    equal = true;
-
-    for (let i = 0; i < a.length; i++) {
-      const aElement = a[i];
-
-      if (!isEqual_(aElement, b[i], aStack, bStack)) {
-        equal = false;
-        break;
-      }
-    }
-  } else if ((0, _underscore.isRegExp)(a) && (0, _underscore.isRegExp)(b)) {
-    equal = (0, _underscore.isEqual)(a, b);
-  } else if ((0, _underscore.isElement)(a) && (0, _underscore.isElement)(b)) {
-    equal = a === b;
-  } else if ((0, _underscore.isObject)(a) && (0, _underscore.isObject)(b)) {
-    const aCtor = a.constructor;
-    const bCtor = b.constructor;
-    const aCtorValid = (0, _underscore.isFunction)(aCtor) && aCtor instanceof aCtor;
-    const bCtorValid = (0, _underscore.isFunction)(bCtor) && bCtor instanceof bCtor;
-
-    if (aCtor !== bCtor && !(aCtorValid && bCtorValid)) {
-      equal = false;
-    } else {
-      let key;
-      let aKeyCount = 0;
-      equal = true;
-
-      for (key in a) {
-        const aValue = a[key];
-
-        if (!(0, _underscore.has)(a, key)) {
-          continue;
-        }
-
-        aKeyCount++;
-
-        if (!(0, _underscore.has)(b, key) || !isEqual_(aValue, b[key], aStack, bStack)) {
-          equal = false;
-          break;
-        }
-      }
-
-      if (equal) {
-        let bKeyCount = 0;
-
-        for (key in b) {
-          const bValue = b[key];
-
-          if ((0, _underscore.has)(b, key)) {
-            bKeyCount++;
-          }
-        }
-
-        equal = aKeyCount === bKeyCount;
-      }
-    }
-  } else {
-    equal = (0, _underscore.isEqual)(a, b);
-  }
-
-  aStack.pop();
-  bStack.pop();
-  return equal;
-} // TODO: Consider shorter variations of null checks:
-// https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md#ds207-consider-shorter-variations-of-null-checks
\ No newline at end of file
diff --git a/package.json b/package.json
index 24f55fe..b1959b2 100644
--- a/package.json
+++ b/package.json
@@ -8,15 +8,10 @@
       "url": "http://github.com/atom/underscore-plus/raw/master/LICENSE.md"
     }
   ],
-  "main": "./lib/underscore-plus.js",
+  "main": "./src/underscore-plus.js",
   "scripts": {
-    "clean": "shx rm -rf lib",
     "test": "jasmine-focused --captureExceptions --coffee spec",
-    "lint": "coffeelint spec/*.coffee",
-    "bower": "shx mkdir -p dist && shx cp -r lib/*.js ./dist",
-    "babel": "npm run clean && shx cp -r src lib && cross-env NODE_ENV=development cross-env BABEL_ENV=development babel lib --out-dir lib && shx rm -f lib/*.mjs",
-    "build": "npm run babel",
-    "prepare": "npm run clean && npm run build && npm run bower"
+    "lint": "coffeelint spec/*.coffee"
   },
   "repository": {
     "type": "git",
@@ -34,15 +29,7 @@
   "devDependencies": {
     "@types/underscore": "^1.10.3",
     "jasmine-focused": "1.x",
-    "coffeelint": "^2.1.0",
-    "@babel/cli": "7.10.3",
-    "@babel/core": "7.10.3",
-    "@babel/plugin-proposal-export-namespace-from": "^7.10.4",
-    "@babel/plugin-proposal-nullish-coalescing-operator": "^7.10.4",
-    "@babel/plugin-proposal-optional-chaining": "^7.10.4",
-    "@babel/plugin-transform-modules-commonjs": "^7.10.4",
-    "shx": "^0.3.2",
-    "cross-env": "^7.0.2"
+    "coffeelint": "^2.1.0"
   },
   "coffeelintConfig": {
     "no_empty_param_list": {
diff --git a/spec/underscore-plus-spec.coffee b/spec/underscore-plus-spec.coffee
index 541f393..76226af 100644
--- a/spec/underscore-plus-spec.coffee
+++ b/spec/underscore-plus-spec.coffee
@@ -1,4 +1,4 @@
-_ = require '../lib/underscore-plus.js'
+_ = require '../src/underscore-plus.js'
 
 describe "underscore extensions", ->
   describe "::adviseBefore(object, methodName, advice)", ->
diff --git a/src/underscore-plus.js b/src/underscore-plus.js
new file mode 100644
index 0000000..31e626f
--- /dev/null
+++ b/src/underscore-plus.js
@@ -0,0 +1,430 @@
+const {every, flatten, has, include, isArray, isElement, isEqual: _isEqual, isFunction, isObject, isRegExp, uniq } = require("underscore");
+
+const macModifierKeyMap = {
+  cmd: '\u2318',
+  ctrl: '\u2303',
+  alt: '\u2325',
+  option: '\u2325',
+  shift: '\u21e7',
+  enter: '\u23ce',
+  left: '\u2190',
+  right: '\u2192',
+  up: '\u2191',
+  down: '\u2193',
+  cmdorctrl: '\u2318'
+};
+
+const nonMacModifierKeyMap = {
+  cmd: 'Cmd',
+  ctrl: 'Ctrl',
+  alt: 'Alt',
+  option: 'Alt',
+  shift: 'Shift',
+  enter: 'Enter',
+  left: 'Left',
+  right: 'Right',
+  up: 'Up',
+  down: 'Down',
+  cmdorctrl: 'Ctrl'
+};
+
+// Human key combos should always explicitly state the shift key. This map is a disambiguator.
+// 'shift-version': 'no-shift-version'
+const shiftKeyMap = {
+  '~': '`',
+  '_': '-',
+  '+': '=',
+  '|': '\\',
+  '{': '[',
+  '}': ']',
+  ':': ';',
+  '"': '\'',
+  '<': ',',
+  '>': '.',
+  '?': '/'
+};
+
+function splitKeyPath(keyPath) {
+  let startIndex = 0;
+  const keyPathArray = [];
+  if (keyPath == null) { return keyPathArray; }
+  for (let i = 0; i < keyPath.length; i++) {
+    const char = keyPath[i];
+    if ((char === '.') && ((i === 0) || (keyPath[i-1] !== '\\'))) {
+      keyPathArray.push(keyPath.substring(startIndex, i));
+      startIndex = i + 1;
+    }
+  }
+  keyPathArray.push(keyPath.substr(startIndex, keyPath.length));
+  return keyPathArray;
+}
+
+const isPlainObject = value => isObject(value) && !isArray(value);
+
+function isEqual_(a, b, aStack=[], bStack=[]) {
+  if (a === b) { return _isEqual(a, b); }
+  if (isFunction(a) || isFunction(b)) { return _isEqual(a, b); }
+
+  let stackIndex = aStack.length;
+  while (stackIndex--) {
+    if (aStack[stackIndex] === a) { return bStack[stackIndex] === b; }
+  }
+  aStack.push(a);
+  bStack.push(b);
+
+  let equal = false;
+  if (isFunction(a?.isEqual)) {
+    equal = a.isEqual(b, aStack, bStack);
+  } else if (isFunction(b?.isEqual)) {
+    equal = b.isEqual(a, bStack, aStack);
+  } else if (isArray(a) && isArray(b) && (a.length === b.length)) {
+    equal = true;
+    for (let i = 0; i < a.length; i++) {
+      const aElement = a[i];
+      if (!isEqual_(aElement, b[i], aStack, bStack)) {
+        equal = false;
+        break;
+      }
+    }
+  } else if (isRegExp(a) && isRegExp(b)) {
+    equal = _isEqual(a, b);
+  } else if (isElement(a) && isElement(b)) {
+    equal = a === b;
+  } else if (isObject(a) && isObject(b)) {
+    const aCtor = a.constructor;
+    const bCtor = b.constructor;
+    const aCtorValid = isFunction(aCtor) && aCtor instanceof aCtor;
+    const bCtorValid = isFunction(bCtor) && bCtor instanceof bCtor;
+    if ((aCtor !== bCtor) && !(aCtorValid && bCtorValid)) {
+      equal = false;
+    } else {
+      let key;
+      let aKeyCount = 0;
+      equal = true;
+      for (key in a) {
+        const aValue = a[key];
+        if (!has(a, key)) { continue; }
+        aKeyCount++;
+        if (!has(b, key) || !isEqual_(aValue, b[key], aStack, bStack)) {
+          equal = false;
+          break;
+        }
+      }
+      if (equal) {
+        let bKeyCount = 0;
+        for (key in b) {
+          const bValue = b[key];
+          if (has(b, key)) { bKeyCount++; }
+        }
+        equal = aKeyCount === bKeyCount;
+      }
+    }
+  } else {
+    equal = _isEqual(a, b);
+  }
+
+  aStack.pop();
+  bStack.pop();
+  return equal;
+}
+
+module.exports = {
+  ...require("underscore"),
+  adviseBefore(object, methodName, advice) {
+    const original = object[methodName];
+    return object[methodName] = function(...args) {
+      if (advice.apply(this, args) !== false) {
+        return original.apply(this, args);
+      }
+    };
+  },
+  camelize(string) {
+    if (string) {
+      return string.replace(/[_-]+(\w)/g, m => m[1].toUpperCase());
+    } else {
+      return '';
+    }
+  },
+  capitalize(word) {
+    if (!word) { return ''; }
+
+    if (word.toLowerCase() === 'github') {
+      return 'GitHub';
+    } else {
+      return word[0].toUpperCase() + word.slice(1);
+    }
+  },
+  compactObject(object) {
+    const newObject = {};
+    for (let key in object) {
+      const value = object[key];
+      if (value != null) { newObject[key] = value; }
+    }
+    return newObject;
+  },
+  dasherize(string) {
+    if (!string) { return ''; }
+
+    string = string[0].toLowerCase() + string.slice(1);
+    return string.replace(/([A-Z])|(_)/g, function(m, letter) {
+      if (letter) {
+        return "-" + letter.toLowerCase();
+      } else {
+        return "-";
+      }
+    });
+  },
+  // Deep clones the given JSON object.
+  //
+  // `object` - The JSON object to clone.
+  //
+  // Returns a deep clone of the JSON object.
+  deepClone(object) {
+    if (isArray(object)) {
+      return object.map(value => this.deepClone(value));
+    } else if (isObject(object) && !isFunction(object)) {
+      return this.mapObject(object, (key, value) => [key, this.deepClone(value)]);
+    } else {
+      return object;
+    }
+  },
+  deepExtend(target) {
+    let result = target;
+    let i = 0;
+    while (++i < arguments.length) {
+      const object = arguments[i];
+      if (isPlainObject(result) && isPlainObject(object)) {
+        const keys = Object.keys(object)
+        for (let key of keys) {
+          result[key] = this.deepExtend(result[key], object[key]);
+        }
+      } else {
+        result = this.deepClone(object);
+      }
+    }
+    return result;
+  },
+  deepContains(array, target) {
+    if (array == null) { return false; }
+    for (let object of array) {
+      if (_isEqual(object, target)) { return true; }
+    }
+    return false;
+  },
+  endsWith(string, suffix) {
+    if (suffix == null) { suffix = ''; }
+    if (string) {
+      return string.indexOf(suffix, string.length - suffix.length) !== -1;
+    } else {
+      return false;
+    }
+  },
+  escapeAttribute(string) {
+    if (string) {
+      return string.replace(/"/g, '&quot;').replace(/\n/g, '').replace(/\\/g, '-');
+    } else {
+      return '';
+    }
+  },
+  escapeRegExp(string) {
+    if (string) {
+      return string.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&');
+    } else {
+      return '';
+    }
+  },
+  humanizeEventName(eventName, eventDoc) {
+    const [namespace, event]  = eventName.split(':');
+    if (event == null) { return this.undasherize(namespace); }
+
+    const namespaceDoc = this.undasherize(namespace);
+    if (eventDoc == null) { eventDoc = this.undasherize(event); }
+
+    return `${namespaceDoc}: ${eventDoc}`;
+  },
+  humanizeKey(key, platform=process.platform) {
+    if (!key) { return key; }
+
+    const modifierKeyMap = platform === 'darwin' ? macModifierKeyMap : nonMacModifierKeyMap;
+
+    if (modifierKeyMap[key]) {
+      return modifierKeyMap[key];
+    } else if ((key.length === 1) && (shiftKeyMap[key] != null)) {
+      return [modifierKeyMap.shift, shiftKeyMap[key]];
+    } else if ((key.length === 1) && (key === key.toUpperCase()) && (key.toUpperCase() !== key.toLowerCase())) {
+      return [modifierKeyMap.shift, key.toUpperCase()];
+    } else if ((key.length === 1) || /f[0-9]{1,2}/.test(key)) {
+      return key.toUpperCase();
+    } else {
+      if (platform === 'darwin') {
+        return key;
+      } else {
+        return this.capitalize(key);
+      }
+    }
+  },
+  // Humanize the keystroke according to platform conventions. This method
+  // attempts to mirror the text the given keystroke would have if displayed in
+  // a system menu.
+  //
+  // keystroke - A String keystroke to humanize such as `ctrl-O`.
+  // platform  - An optional String platform to humanize for (default:
+  //             `process.platform`).
+  //
+  // Returns a humanized representation of the keystroke.
+  humanizeKeystroke(keystroke, platform=process.platform) {
+    if (!keystroke) { return keystroke; }
+
+    const keystrokes = keystroke.split(' ');
+    const humanizedKeystrokes = [];
+    for (keystroke of keystrokes) {
+      let keys = [];
+      const splitKeystroke = keystroke.split('-');
+      for (let index = 0; index < splitKeystroke.length; index++) {
+        // Check for consecutive dashes such as cmd--
+        let key = splitKeystroke[index];
+        if ((key === '') && (splitKeystroke[index-1] === '')) { key = '-'; }
+        if (key) { keys.push(this.humanizeKey(key, platform)); }
+      }
+
+      keys = uniq(flatten(keys));
+      if (platform === 'darwin') {
+        keys = keys.join('');
+      } else {
+        keys = keys.join('+');
+      }
+      humanizedKeystrokes.push(keys);
+    }
+
+    return humanizedKeystrokes.join(' ');
+  },
+  isSubset(potentialSubset, potentialSuperset) {
+    return every(potentialSubset, element => include(potentialSuperset, element));
+  },
+  losslessInvert(hash) {
+    const inverted = {};
+    for (let key in hash) {
+      const value = hash[key];
+      if (inverted[value] == null) { inverted[value] = []; }
+      inverted[value].push(key);
+    }
+    return inverted;
+  },
+  // Transform the given object into another object.
+  //
+  // `object` - The object to transform.
+  // `iterator` -
+  //   A function that takes `(key, value)` arguments and returns a
+  //   `[key, value]` tuple.
+  //
+  // Returns a new object based with the key/values returned by the iterator.
+  mapObject(object, iterator) {
+    const newObject = {};
+    const keys = Object.keys(object)
+    for (let key of keys) {
+      let value;
+      [key, value] = iterator(key, object[key]);
+      newObject[key] = value;
+    }
+
+    return newObject;
+  },
+  multiplyString(string, n) {
+    let finalString = "";
+    let i = 0;
+    while (i < n) {
+      finalString += string;
+      i++;
+    }
+    return finalString;
+  },
+  pluralize(count=0, singular, plural=singular+'s') {
+    if (count === 1) {
+      return `${count} ${singular}`;
+    } else {
+      return `${count} ${plural}`;
+    }
+  },
+  remove(array, element) {
+    const index = array.indexOf(element);
+    if (index >= 0) { array.splice(index, 1); }
+    return array;
+  },
+  setValueForKeyPath(object, keyPath, value) {
+    const keys = splitKeyPath(keyPath);
+    while (keys.length > 1) {
+      const key = keys.shift();
+      if (object[key] == null) { object[key] = {}; }
+      object = object[key];
+    }
+    if (value != null) {
+      object[keys.shift()] = value;
+    } else {
+      delete object[keys.shift()];
+    }
+  },
+  hasKeyPath(object, keyPath) {
+    const keys = splitKeyPath(keyPath);
+    for (let key of keys) {
+      if (!object.hasOwnProperty(key)) { return false; }
+      object = object[key];
+    }
+    return true;
+  },
+  spliceWithArray(originalArray, start, length, insertedArray, chunkSize=100000) {
+    if (insertedArray.length < chunkSize) {
+      originalArray.splice(start, length, ...insertedArray);
+    } else {
+        originalArray.splice(start, length);
+        for (let chunkStart = 0, end = insertedArray.length;  chunkStart <= end; chunkStart += chunkSize) {
+          originalArray.splice(start + chunkStart, 0, ...insertedArray.slice(chunkStart, chunkStart + chunkSize));
+        }
+    }
+  },
+  sum(array) {
+    let sum = 0;
+    for (let elt of array) { sum += elt; }
+    return sum;
+  },
+  uncamelcase(string) {
+    if (!string) { return ''; }
+
+    const result = string.replace(/([A-Z])|_+/g, (match, letter='') => ` ${letter}`);
+    return this.capitalize(result.trim());
+  },
+  undasherize(string) {
+    if (string) {
+      return string.split('-').map(this.capitalize).join(' ');
+    } else {
+      return '';
+    }
+  },
+  underscore(string) {
+    if (!string) { return ''; }
+
+    string = string[0].toLowerCase() + string.slice(1);
+    return string.replace(/([A-Z])|-+/g, (match, letter='') => `_${letter.toLowerCase()}`);
+  },
+  valueForKeyPath(object, keyPath) {
+    const keys = splitKeyPath(keyPath);
+    for (let key of keys) {
+      object = object[key];
+      if (object == null) { return; }
+    }
+    return object;
+  },
+  isEqual(a, b, aStack, bStack) {
+    if (isArray(aStack) && isArray(bStack)) {
+      return isEqual_(a, b, aStack, bStack);
+    } else {
+      return isEqual_(a, b);
+    }
+  },
+  isEqualForProperties(a, b, ...properties) {
+    // TODO is Array.from needed?
+    for (let property of Array.from(properties)) {
+      if (!_isEqual(a[property], b[property])) { return false; }
+    }
+    return true;
+  }
+};
diff --git a/src/underscore-plus.mjs b/src/underscore-plus.mjs
deleted file mode 100644
index cda78b5..0000000
--- a/src/underscore-plus.mjs
+++ /dev/null
@@ -1,462 +0,0 @@
-export * from 'underscore'
-
-// import * as _ from 'underscore' // if we needed all
-import {every, flatten, has, include, isArray, isElement, isEqual as _isEqual, isFunction, isObject, isRegExp, uniq} from "underscore";
-
-const macModifierKeyMap = {
-  cmd: '\u2318',
-  ctrl: '\u2303',
-  alt: '\u2325',
-  option: '\u2325',
-  shift: '\u21e7',
-  enter: '\u23ce',
-  left: '\u2190',
-  right: '\u2192',
-  up: '\u2191',
-  down: '\u2193',
-  cmdorctrl: '\u2318'
-};
-
-const nonMacModifierKeyMap = {
-  cmd: 'Cmd',
-  ctrl: 'Ctrl',
-  alt: 'Alt',
-  option: 'Alt',
-  shift: 'Shift',
-  enter: 'Enter',
-  left: 'Left',
-  right: 'Right',
-  up: 'Up',
-  down: 'Down',
-  cmdorctrl: 'Ctrl'
-};
-
-// Human key combos should always explicitly state the shift key. This map is a disambiguator.
-// 'shift-version': 'no-shift-version'
-const shiftKeyMap = {
-  '~': '`',
-  '_': '-',
-  '+': '=',
-  '|': '\\',
-  '{': '[',
-  '}': ']',
-  ':': ';',
-  '"': '\'',
-  '<': ',',
-  '>': '.',
-  '?': '/'
-};
-
-function splitKeyPath(keyPath) {
-  let startIndex = 0;
-  const keyPathArray = [];
-  if (keyPath == null) { return keyPathArray; }
-  for (let i = 0; i < keyPath.length; i++) {
-    const char = keyPath[i];
-    if ((char === '.') && ((i === 0) || (keyPath[i-1] !== '\\'))) {
-      keyPathArray.push(keyPath.substring(startIndex, i));
-      startIndex = i + 1;
-    }
-  }
-  keyPathArray.push(keyPath.substr(startIndex, keyPath.length));
-  return keyPathArray;
-}
-
-const isPlainObject = value => isObject(value) && !isArray(value);
-
-export function adviseBefore(object, methodName, advice) {
-  const original = object[methodName];
-  return object[methodName] = function(...args) {
-    if (advice.apply(this, args) !== false) {
-      return original.apply(this, args);
-    }
-  };
-}
-
-export function camelize(string) {
-  if (string) {
-    return string.replace(/[_-]+(\w)/g, m => m[1].toUpperCase());
-  } else {
-    return '';
-  }
-}
-
-export function capitalize(word) {
-  if (!word) { return ''; }
-
-  if (word.toLowerCase() === 'github') {
-    return 'GitHub';
-  } else {
-    return word[0].toUpperCase() + word.slice(1);
-  }
-}
-
-export function compactObject(object) {
-  const newObject = {};
-  for (let key in object) {
-    const value = object[key];
-    if (value != null) { newObject[key] = value; }
-  }
-  return newObject;
-}
-
-export function dasherize(string) {
-  if (!string) { return ''; }
-
-  string = string[0].toLowerCase() + string.slice(1);
-  return string.replace(/([A-Z])|(_)/g, function(m, letter) {
-    if (letter) {
-      return "-" + letter.toLowerCase();
-    } else {
-      return "-";
-    }
-  });
-}
-
-// Deep clones the given JSON object.
-//
-// `object` - The JSON object to clone.
-//
-// Returns a deep clone of the JSON object.
-export function deepClone(object) {
-  if (isArray(object)) {
-    return object.map(value => deepClone(value));
-  } else if (isObject(object) && !isFunction(object)) {
-    return mapObject(object, (key, value) => [key, deepClone(value)]);
-  } else {
-    return object;
-  }
-}
-
-export function deepExtend(target) {
-  let result = target;
-  let i = 0;
-  while (++i < arguments.length) {
-    const object = arguments[i];
-    if (isPlainObject(result) && isPlainObject(object)) {
-      const keys = Object.keys(object)
-      for (let key of keys) {
-        result[key] = deepExtend(result[key], object[key]);
-      }
-    } else {
-      result = deepClone(object);
-    }
-  }
-  return result;
-}
-
-export function deepContains(array, target) {
-  if (array == null) { return false; }
-  for (let object of array) {
-    if (_isEqual(object, target)) { return true; }
-  }
-  return false;
-}
-
-export function endsWith(string, suffix) {
-  if (suffix == null) { suffix = ''; }
-  if (string) {
-    return string.indexOf(suffix, string.length - suffix.length) !== -1;
-  } else {
-    return false;
-  }
-}
-
-export function escapeAttribute(string) {
-  if (string) {
-    return string.replace(/"/g, '&quot;').replace(/\n/g, '').replace(/\\/g, '-');
-  } else {
-    return '';
-  }
-}
-
-export function escapeRegExp(string) {
-  if (string) {
-    return string.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&');
-  } else {
-    return '';
-  }
-}
-
-export function humanizeEventName(eventName, eventDoc) {
-  const [namespace, event]  = eventName.split(':');
-  if (event == null) { return undasherize(namespace); }
-
-  const namespaceDoc = undasherize(namespace);
-  if (eventDoc == null) { eventDoc = undasherize(event); }
-
-  return `${namespaceDoc}: ${eventDoc}`;
-}
-
-export function humanizeKey(key, platform=process.platform) {
-  if (!key) { return key; }
-
-  const modifierKeyMap = platform === 'darwin' ? macModifierKeyMap : nonMacModifierKeyMap;
-
-  if (modifierKeyMap[key]) {
-    return modifierKeyMap[key];
-  } else if ((key.length === 1) && (shiftKeyMap[key] != null)) {
-    return [modifierKeyMap.shift, shiftKeyMap[key]];
-  } else if ((key.length === 1) && (key === key.toUpperCase()) && (key.toUpperCase() !== key.toLowerCase())) {
-    return [modifierKeyMap.shift, key.toUpperCase()];
-  } else if ((key.length === 1) || /f[0-9]{1,2}/.test(key)) {
-    return key.toUpperCase();
-  } else {
-    if (platform === 'darwin') {
-      return key;
-    } else {
-      return capitalize(key);
-    }
-  }
-}
-
-// Humanize the keystroke according to platform conventions. This method
-// attempts to mirror the text the given keystroke would have if displayed in
-// a system menu.
-//
-// keystroke - A String keystroke to humanize such as `ctrl-O`.
-// platform  - An optional String platform to humanize for (default:
-//             `process.platform`).
-//
-// Returns a humanized representation of the keystroke.
-export function humanizeKeystroke(keystroke, platform=process.platform) {
-    if (!keystroke) { return keystroke; }
-
-  const keystrokes = keystroke.split(' ');
-  const humanizedKeystrokes = [];
-  for (keystroke of keystrokes) {
-    let keys = [];
-    const splitKeystroke = keystroke.split('-');
-    for (let index = 0; index < splitKeystroke.length; index++) {
-      // Check for consecutive dashes such as cmd--
-      let key = splitKeystroke[index];
-      if ((key === '') && (splitKeystroke[index-1] === '')) { key = '-'; }
-      if (key) { keys.push(humanizeKey(key, platform)); }
-    }
-
-    keys = uniq(flatten(keys));
-    if (platform === 'darwin') {
-      keys = keys.join('');
-    } else {
-      keys = keys.join('+');
-    }
-    humanizedKeystrokes.push(keys);
-  }
-
-  return humanizedKeystrokes.join(' ');
-}
-
-export function isSubset(potentialSubset, potentialSuperset) {
-  return every(potentialSubset, element => include(potentialSuperset, element));
-}
-
-export function losslessInvert(hash) {
-  const inverted = {};
-  for (let key in hash) {
-    const value = hash[key];
-    if (inverted[value] == null) { inverted[value] = []; }
-    inverted[value].push(key);
-  }
-  return inverted;
-}
-
-// Transform the given object into another object.
-//
-// `object` - The object to transform.
-// `iterator` -
-//   A function that takes `(key, value)` arguments and returns a
-//   `[key, value]` tuple.
-//
-// Returns a new object based with the key/values returned by the iterator.
-export function mapObject(object, iterator) {
-  const newObject = {};
-  const keys = Object.keys(object)
-  for (let key of keys) {
-    let value;
-    [key, value] = iterator(key, object[key]);
-    newObject[key] = value;
-  }
-
-  return newObject;
-}
-
-export function multiplyString(string, n) {
-  let finalString = "";
-  let i = 0;
-  while (i < n) {
-    finalString += string;
-    i++;
-  }
-  return finalString;
-}
-
-export function pluralize(count=0, singular, plural=singular+'s') {
-  if (count === 1) {
-    return `${count} ${singular}`;
-  } else {
-    return `${count} ${plural}`;
-  }
-}
-
-export function remove(array, element) {
-  const index = array.indexOf(element);
-  if (index >= 0) { array.splice(index, 1); }
-  return array;
-}
-
-export function setValueForKeyPath(object, keyPath, value) {
-  const keys = splitKeyPath(keyPath);
-  while (keys.length > 1) {
-    const key = keys.shift();
-    if (object[key] == null) { object[key] = {}; }
-    object = object[key];
-  }
-  if (value != null) {
-    object[keys.shift()] = value;
-  } else {
-    delete object[keys.shift()];
-  }
-}
-
-export function hasKeyPath(object, keyPath) {
-  const keys = splitKeyPath(keyPath);
-  for (let key of keys) {
-    if (!object.hasOwnProperty(key)) { return false; }
-    object = object[key];
-  }
-  return true;
-}
-
-export function spliceWithArray(originalArray, start, length, insertedArray, chunkSize=100000) {
-  if (insertedArray.length < chunkSize) {
-    originalArray.splice(start, length, ...insertedArray);
-  } else {
-      originalArray.splice(start, length);
-      for (let chunkStart = 0, end = insertedArray.length;  chunkStart <= end; chunkStart += chunkSize) {
-        originalArray.splice(start + chunkStart, 0, ...insertedArray.slice(chunkStart, chunkStart + chunkSize));
-      }
-  }
-}
-
-export function sum(array) {
-  let sum = 0;
-  for (let elt of array) { sum += elt; }
-  return sum;
-}
-
-export function uncamelcase(string) {
-  if (!string) { return ''; }
-
-  const result = string.replace(/([A-Z])|_+/g, (match, letter='') => ` ${letter}`);
-  return capitalize(result.trim());
-}
-
-export function undasherize(string) {
-  if (string) {
-    return string.split('-').map(capitalize).join(' ');
-  } else {
-    return '';
-  }
-}
-
-export function underscore(string) {
-  if (!string) { return ''; }
-
-  string = string[0].toLowerCase() + string.slice(1);
-  return string.replace(/([A-Z])|-+/g, (match, letter='') => `_${letter.toLowerCase()}`);
-}
-
-export function valueForKeyPath(object, keyPath) {
-  const keys = splitKeyPath(keyPath);
-  for (let key of keys) {
-    object = object[key];
-    if (object == null) { return; }
-  }
-  return object;
-}
-
-export function isEqual(a, b, aStack, bStack) {
-  if (isArray(aStack) && isArray(bStack)) {
-    return isEqual_(a, b, aStack, bStack);
-  } else {
-    return isEqual_(a, b);
-  }
-}
-
-export function isEqualForProperties(a, b, ...properties) {
-  // TODO is Array.from needed?
-  for (let property of Array.from(properties)) {
-    if (!_isEqual(a[property], b[property])) { return false; }
-  }
-  return true;
-}
-
-function isEqual_(a, b, aStack=[], bStack=[]) {
-  if (a === b) { return _isEqual(a, b); }
-  if (isFunction(a) || isFunction(b)) { return _isEqual(a, b); }
-
-  let stackIndex = aStack.length;
-  while (stackIndex--) {
-    if (aStack[stackIndex] === a) { return bStack[stackIndex] === b; }
-  }
-  aStack.push(a);
-  bStack.push(b);
-
-  let equal = false;
-  if (isFunction(a?.isEqual)) {
-    equal = a.isEqual(b, aStack, bStack);
-  } else if (isFunction(b?.isEqual)) {
-    equal = b.isEqual(a, bStack, aStack);
-  } else if (isArray(a) && isArray(b) && (a.length === b.length)) {
-    equal = true;
-    for (let i = 0; i < a.length; i++) {
-      const aElement = a[i];
-      if (!isEqual_(aElement, b[i], aStack, bStack)) {
-        equal = false;
-        break;
-      }
-    }
-  } else if (isRegExp(a) && isRegExp(b)) {
-    equal = _isEqual(a, b);
-  } else if (isElement(a) && isElement(b)) {
-    equal = a === b;
-  } else if (isObject(a) && isObject(b)) {
-    const aCtor = a.constructor;
-    const bCtor = b.constructor;
-    const aCtorValid = isFunction(aCtor) && aCtor instanceof aCtor;
-    const bCtorValid = isFunction(bCtor) && bCtor instanceof bCtor;
-    if ((aCtor !== bCtor) && !(aCtorValid && bCtorValid)) {
-      equal = false;
-    } else {
-      let key;
-      let aKeyCount = 0;
-      equal = true;
-      for (key in a) {
-        const aValue = a[key];
-        if (!has(a, key)) { continue; }
-        aKeyCount++;
-        if (!has(b, key) || !isEqual_(aValue, b[key], aStack, bStack)) {
-          equal = false;
-          break;
-        }
-      }
-      if (equal) {
-        let bKeyCount = 0;
-        for (key in b) {
-          const bValue = b[key];
-          if (has(b, key)) { bKeyCount++; }
-        }
-        equal = aKeyCount === bKeyCount;
-      }
-    }
-  } else {
-    equal = _isEqual(a, b);
-  }
-
-  aStack.pop();
-  bStack.pop();
-  return equal;
-}
-
-// TODO: Consider shorter variations of null checks:
-// https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md#ds207-consider-shorter-variations-of-null-checks