Continue to use more ES2015.

_setToPairs.js

@@ -6,12 +6,12 @@
  * @returns {Array} Returns the value-value pairs.
  */
 function setToPairs(set) {
-  var index = -1,
-      result = Array(set.size);
+  let index = -1;
+  const result = Array(set.size);
 
-  set.forEach(function(value) {
-    result[++index] = [value, value];
-  });
+  set.forEach(value =>
+    result[++index] = [value, value]
+  );
   return result;
 }
 

partition.js

@@ -36,8 +36,7 @@ import createAggregator from './_createAggregator.js';
  * _.partition(users, 'active');
  * // => objects for [['fred'], ['barney', 'pebbles']]
  */
-var partition = createAggregator(function(result, value, key) {
-  result[key ? 0 : 1].push(value);
-}, function() { return [[], []]; });
+const partition = createAggregator((result, value, key) =>
+  result[key ? 0 : 1].push(value), () => [[], []]);
 
 export default partition;

union.js

@@ -18,7 +18,8 @@ import isArrayLikeObject from './isArrayLikeObject.js';
  * _.union([2], [1, 2]);
  * // => [2, 1]
  */
-const union = (...arrays) =>
-  baseUniq(baseFlatten(arrays, 1, isArrayLikeObject, true));
+function union(...arrays) {
+  return baseUniq(baseFlatten(arrays, 1, isArrayLikeObject, true));
+}
 
 export default union;

unionBy.js

@@ -27,12 +27,12 @@ import last from './last.js';
  * _.unionBy([{ 'x': 1 }], [{ 'x': 2 }, { 'x': 1 }], 'x');
  * // => [{ 'x': 1 }, { 'x': 2 }]
  */
-const unionBy = (...arrays) => {
+function unionBy(...arrays) {
   let iteratee = last(arrays);
   if (isArrayLikeObject(iteratee)) {
     iteratee = undefined;
   }
   return baseUniq(baseFlatten(arrays, 1, isArrayLikeObject, true), baseIteratee(iteratee, 2));
-};
+}
 
 export default unionBy;

xor.js

@@ -20,7 +20,8 @@ import isArrayLikeObject from './isArrayLikeObject.js';
  * _.xor([2, 1], [2, 3]);
  * // => [1, 3]
  */
-const xor = (...arrays) =>
-  baseXor(arrayFilter(arrays, isArrayLikeObject));
+function xor(...arrays) {
+  return baseXor(arrayFilter(arrays, isArrayLikeObject));
+}
 
 export default xor;

xorBy.js

@@ -27,12 +27,12 @@ import last from './last.js';
  * _.xorBy([{ 'x': 1 }], [{ 'x': 2 }, { 'x': 1 }], 'x');
  * // => [{ 'x': 2 }]
  */
-const xorBy = (...arrays) => {
+function xorBy(...arrays) {
   let iteratee = last(arrays);
   if (isArrayLikeObject(iteratee)) {
     iteratee = undefined;
   }
   return baseXor(arrayFilter(arrays, isArrayLikeObject), baseIteratee(iteratee, 2));
-};
+}
 
 export default xorBy;

zipWith.js

@@ -1,4 +1,3 @@
-import baseRest from './_baseRest.js';
 import unzipWith from './unzipWith.js';
 
 /**
@@ -21,12 +20,12 @@ import unzipWith from './unzipWith.js';
  * });
  * // => [111, 222]
  */
-var zipWith = baseRest(function(arrays) {
-  var length = arrays.length,
-      iteratee = length > 1 ? arrays[length - 1] : undefined;
+function zipWith(...arrays) {
+  const length = arrays.length;
+  let iteratee = length > 1 ? arrays[length - 1] : undefined;
 
   iteratee = typeof iteratee == 'function' ? (arrays.pop(), iteratee) : undefined;
   return unzipWith(arrays, iteratee);
-});
+}
 
 export default zipWith;