diff --git a/_DataView.js b/_DataView.js
index 1bbaaa190..a87db7d07 100644
--- a/_DataView.js
+++ b/_DataView.js
@@ -2,6 +2,6 @@ import getNative from './_getNative.js';
 import root from './_root.js';
 
 /* Built-in method references that are verified to be native. */
-var DataView = getNative(root, 'DataView');
+const DataView = getNative(root, 'DataView');
 
 export default DataView;
diff --git a/_Hash.js b/_Hash.js
index 8ecacb008..db6e0142f 100644
--- a/_Hash.js
+++ b/_Hash.js
@@ -12,12 +12,12 @@ import hashSet from './_hashSet.js';
  * @param {Array} [entries] The key-value pairs to cache.
  */
 function Hash(entries) {
-  var index = -1,
-      length = entries == null ? 0 : entries.length;
+  let index = -1;
+  const length = entries == null ? 0 : entries.length;
 
   this.clear();
   while (++index < length) {
-    var entry = entries[index];
+    const entry = entries[index];
     this.set(entry[0], entry[1]);
   }
 }
diff --git a/_arrayAggregator.js b/_arrayAggregator.js
index d45187929..eb0f3edf8 100644
--- a/_arrayAggregator.js
+++ b/_arrayAggregator.js
@@ -9,11 +9,11 @@
  * @returns {Function} Returns `accumulator`.
  */
 function arrayAggregator(array, setter, iteratee, accumulator) {
-  var index = -1,
-      length = array == null ? 0 : array.length;
+  let index = -1;
+  const length = array == null ? 0 : array.length;
 
   while (++index < length) {
-    var value = array[index];
+    const value = array[index];
     setter(accumulator, value, iteratee(value), array);
   }
   return accumulator;
diff --git a/_arrayEach.js b/_arrayEach.js
index 2a570bf7f..0158205ee 100644
--- a/_arrayEach.js
+++ b/_arrayEach.js
@@ -8,8 +8,8 @@
  * @returns {Array} Returns `array`.
  */
 function arrayEach(array, iteratee) {
-  var index = -1,
-      length = array == null ? 0 : array.length;
+  let index = -1;
+  const length = array == null ? 0 : array.length;
 
   while (++index < length) {
     if (iteratee(array[index], index, array) === false) {
diff --git a/_arrayEachRight.js b/_arrayEachRight.js
index ce87d1acc..713406c15 100644
--- a/_arrayEachRight.js
+++ b/_arrayEachRight.js
@@ -8,7 +8,7 @@
  * @returns {Array} Returns `array`.
  */
 function arrayEachRight(array, iteratee) {
-  var length = array == null ? 0 : array.length;
+  let length = array == null ? 0 : array.length;
 
   while (length--) {
     if (iteratee(array[length], length, array) === false) {
diff --git a/_arrayEvery.js b/_arrayEvery.js
index 93f30a9bc..a24e76600 100644
--- a/_arrayEvery.js
+++ b/_arrayEvery.js
@@ -9,8 +9,8 @@
  *  else `false`.
  */
 function arrayEvery(array, predicate) {
-  var index = -1,
-      length = array == null ? 0 : array.length;
+  let index = -1;
+  const length = array == null ? 0 : array.length;
 
   while (++index < length) {
     if (!predicate(array[index], index, array)) {
diff --git a/_arrayFilter.js b/_arrayFilter.js
index 20d376994..84b6e7e28 100644
--- a/_arrayFilter.js
+++ b/_arrayFilter.js
@@ -8,13 +8,13 @@
  * @returns {Array} Returns the new filtered array.
  */
 function arrayFilter(array, predicate) {
-  var index = -1,
-      length = array == null ? 0 : array.length,
-      resIndex = 0,
-      result = [];
+  let index = -1;
+  let resIndex = 0;
+  const length = array == null ? 0 : array.length;
+  const result = [];
 
   while (++index < length) {
-    var value = array[index];
+    const value = array[index];
     if (predicate(value, index, array)) {
       result[resIndex++] = value;
     }
diff --git a/_arrayIncludes.js b/_arrayIncludes.js
index d515af900..894511a6a 100644
--- a/_arrayIncludes.js
+++ b/_arrayIncludes.js
@@ -10,7 +10,7 @@ import baseIndexOf from './_baseIndexOf.js';
  * @returns {boolean} Returns `true` if `target` is found, else `false`.
  */
 function arrayIncludes(array, value) {
-  var length = array == null ? 0 : array.length;
+  const length = array == null ? 0 : array.length;
   return !!length && baseIndexOf(array, value, 0) > -1;
 }
 
diff --git a/_arrayIncludesWith.js b/_arrayIncludesWith.js
index 9dedaa253..2fb367414 100644
--- a/_arrayIncludesWith.js
+++ b/_arrayIncludesWith.js
@@ -8,8 +8,8 @@
  * @returns {boolean} Returns `true` if `target` is found, else `false`.
  */
 function arrayIncludesWith(array, value, comparator) {
-  var index = -1,
-      length = array == null ? 0 : array.length;
+  let index = -1;
+  const length = array == null ? 0 : array.length;
 
   while (++index < length) {
     if (comparator(value, array[index])) {
diff --git a/_arrayMap.js b/_arrayMap.js
index 8d32a4e65..811f9dbb3 100644
--- a/_arrayMap.js
+++ b/_arrayMap.js
@@ -8,9 +8,9 @@
  * @returns {Array} Returns the new mapped array.
  */
 function arrayMap(array, iteratee) {
-  var index = -1,
-      length = array == null ? 0 : array.length,
-      result = Array(length);
+  let index = -1;
+  const length = array == null ? 0 : array.length;
+  const result = Array(length);
 
   while (++index < length) {
     result[index] = iteratee(array[index], index, array);
diff --git a/_arrayPush.js b/_arrayPush.js
index 3660a7dbc..fec702a09 100644
--- a/_arrayPush.js
+++ b/_arrayPush.js
@@ -7,9 +7,9 @@
  * @returns {Array} Returns `array`.
  */
 function arrayPush(array, values) {
-  var index = -1,
-      length = values.length,
-      offset = array.length;
+  let index = -1;
+  const length = values.length;
+  const offset = array.length;
 
   while (++index < length) {
     array[offset + index] = values[index];
diff --git a/_arrayReduce.js b/_arrayReduce.js
index 58e1df310..15a961582 100644
--- a/_arrayReduce.js
+++ b/_arrayReduce.js
@@ -11,8 +11,8 @@
  * @returns {*} Returns the accumulated value.
  */
 function arrayReduce(array, iteratee, accumulator, initAccum) {
-  var index = -1,
-      length = array == null ? 0 : array.length;
+  let index = -1;
+  const length = array == null ? 0 : array.length;
 
   if (initAccum && length) {
     accumulator = array[++index];
diff --git a/_arrayReduceRight.js b/_arrayReduceRight.js
index c185bebef..63d2ca542 100644
--- a/_arrayReduceRight.js
+++ b/_arrayReduceRight.js
@@ -11,7 +11,7 @@
  * @returns {*} Returns the accumulated value.
  */
 function arrayReduceRight(array, iteratee, accumulator, initAccum) {
-  var length = array == null ? 0 : array.length;
+  let length = array == null ? 0 : array.length;
   if (initAccum && length) {
     accumulator = array[--length];
   }
diff --git a/_arraySample.js b/_arraySample.js
index 008596fc9..d91b3a43d 100644
--- a/_arraySample.js
+++ b/_arraySample.js
@@ -8,7 +8,7 @@ import baseRandom from './_baseRandom.js';
  * @returns {*} Returns the random element.
  */
 function arraySample(array) {
-  var length = array.length;
+  const length = array.length;
   return length ? array[baseRandom(0, length - 1)] : undefined;
 }
 
diff --git a/_arraySome.js b/_arraySome.js
index d66f4c320..afffba804 100644
--- a/_arraySome.js
+++ b/_arraySome.js
@@ -9,8 +9,8 @@
  *  else `false`.
  */
 function arraySome(array, predicate) {
-  var index = -1,
-      length = array == null ? 0 : array.length;
+  let index = -1;
+  const length = array == null ? 0 : array.length;
 
   while (++index < length) {
     if (predicate(array[index], index, array)) {
diff --git a/_asciiSize.js b/_asciiSize.js
index bbf4df436..76f861afa 100644
--- a/_asciiSize.js
+++ b/_asciiSize.js
@@ -7,6 +7,6 @@ import baseProperty from './_baseProperty.js';
  * @param {string} string The string inspect.
  * @returns {number} Returns the string size.
  */
-var asciiSize = baseProperty('length');
+const asciiSize = baseProperty('length');
 
 export default asciiSize;
diff --git a/_asciiWords.js b/_asciiWords.js
index 7840636ba..479f537b6 100644
--- a/_asciiWords.js
+++ b/_asciiWords.js
@@ -1,5 +1,5 @@
 /** Used to match words composed of alphanumeric characters. */
-var reAsciiWord = /[^\x00-\x2f\x3a-\x40\x5b-\x60\x7b-\x7f]+/g;
+const reAsciiWord = /[^\x00-\x2f\x3a-\x40\x5b-\x60\x7b-\x7f]+/g;
 
 /**
  * Splits an ASCII `string` into an array of its words.
diff --git a/_assignValue.js b/_assignValue.js
index c858e92e0..8ec98a086 100644
--- a/_assignValue.js
+++ b/_assignValue.js
@@ -2,10 +2,10 @@ import baseAssignValue from './_baseAssignValue.js';
 import eq from './eq.js';
 
 /** Used for built-in method references. */
-var objectProto = Object.prototype;
+const objectProto = Object.prototype;
 
 /** Used to check objects for own properties. */
-var hasOwnProperty = objectProto.hasOwnProperty;
+const hasOwnProperty = objectProto.hasOwnProperty;
 
 /**
  * Assigns `value` to `key` of `object` if the existing value is not equivalent
@@ -18,7 +18,7 @@ var hasOwnProperty = objectProto.hasOwnProperty;
  * @param {*} value The value to assign.
  */
 function assignValue(object, key, value) {
-  var objValue = object[key];
+  const objValue = object[key];
   if (!(hasOwnProperty.call(object, key) && eq(objValue, value)) ||
       (value === undefined && !(key in object))) {
     baseAssignValue(object, key, value);
diff --git a/_assocIndexOf.js b/_assocIndexOf.js
index 88afb3979..ac0d5888b 100644
--- a/_assocIndexOf.js
+++ b/_assocIndexOf.js
@@ -9,7 +9,7 @@ import eq from './eq.js';
  * @returns {number} Returns the index of the matched value, else `-1`.
  */
 function assocIndexOf(array, key) {
-  var length = array.length;
+  let length = array.length;
   while (length--) {
     if (eq(array[length][0], key)) {
       return length;
diff --git a/_baseAt.js b/_baseAt.js
index 394738914..ce1e3f204 100644
--- a/_baseAt.js
+++ b/_baseAt.js
@@ -9,10 +9,10 @@ import get from './get.js';
  * @returns {Array} Returns the picked elements.
  */
 function baseAt(object, paths) {
-  var index = -1,
-      length = paths.length,
-      result = Array(length),
-      skip = object == null;
+  let index = -1;
+  const length = paths.length;
+  const result = Array(length);
+  const skip = object == null;
 
   while (++index < length) {
     result[index] = skip ? undefined : get(object, paths[index]);
diff --git a/_baseConformsTo.js b/_baseConformsTo.js
index 3406ec5df..c002b023b 100644
--- a/_baseConformsTo.js
+++ b/_baseConformsTo.js
@@ -7,15 +7,15 @@
  * @returns {boolean} Returns `true` if `object` conforms, else `false`.
  */
 function baseConformsTo(object, source, props) {
-  var length = props.length;
+  let length = props.length;
   if (object == null) {
     return !length;
   }
   object = Object(object);
   while (length--) {
-    var key = props[length],
-        predicate = source[key],
-        value = object[key];
+    const key = props[length];
+    const predicate = source[key];
+    const value = object[key];
 
     if ((value === undefined && !(key in object)) || !predicate(value)) {
       return false;
diff --git a/_baseCreate.js b/_baseCreate.js
index bb546324f..19b057a4f 100644
--- a/_baseCreate.js
+++ b/_baseCreate.js
@@ -21,7 +21,7 @@ const baseCreate = (() => {
       return objectCreate(proto);
     }
     object.prototype = proto;
-    var result = new object;
+    const result = new object;
     object.prototype = undefined;
     return result;
   };
diff --git a/_baseEach.js b/_baseEach.js
index 038e9366d..1495f8376 100644
--- a/_baseEach.js
+++ b/_baseEach.js
@@ -9,6 +9,6 @@ import createBaseEach from './_createBaseEach.js';
  * @param {Function} iteratee The function invoked per iteration.
  * @returns {Array|Object} Returns `collection`.
  */
-var baseEach = createBaseEach(baseForOwn);
+const baseEach = createBaseEach(baseForOwn);
 
 export default baseEach;
diff --git a/_baseEachRight.js b/_baseEachRight.js
index 0e4b053de..c722b0557 100644
--- a/_baseEachRight.js
+++ b/_baseEachRight.js
@@ -9,6 +9,6 @@ import createBaseEach from './_createBaseEach.js';
  * @param {Function} iteratee The function invoked per iteration.
  * @returns {Array|Object} Returns `collection`.
  */
-var baseEachRight = createBaseEach(baseForOwnRight, true);
+const baseEachRight = createBaseEach(baseForOwnRight, true);
 
 export default baseEachRight;
diff --git a/_baseExtremum.js b/_baseExtremum.js
index d154c6127..8929cacbf 100644
--- a/_baseExtremum.js
+++ b/_baseExtremum.js
@@ -11,12 +11,12 @@ import isSymbol from './isSymbol.js';
  * @returns {*} Returns the extremum value.
  */
 function baseExtremum(array, iteratee, comparator) {
-  var index = -1,
-      length = array.length;
+  let index = -1;
+  const length = array.length;
 
   while (++index < length) {
-    var value = array[index],
-        current = iteratee(value);
+    const value = array[index];
+    const current = iteratee(value);
 
     if (current != null && (computed === undefined
           ? (current === current && !isSymbol(current))
diff --git a/_baseFill.js b/_baseFill.js
index c7ef26e73..de407866d 100644
--- a/_baseFill.js
+++ b/_baseFill.js
@@ -12,7 +12,7 @@ import toLength from './toLength.js';
  * @returns {Array} Returns `array`.
  */
 function baseFill(array, value, start, end) {
-  var length = array.length;
+  const length = array.length;
 
   start = toInteger(start);
   if (start < 0) {
diff --git a/_baseFindIndex.js b/_baseFindIndex.js
index 860636ee5..26042d78e 100644
--- a/_baseFindIndex.js
+++ b/_baseFindIndex.js
@@ -10,8 +10,8 @@
  * @returns {number} Returns the index of the matched value, else `-1`.
  */
 function baseFindIndex(array, predicate, fromIndex, fromRight) {
-  var length = array.length,
-      index = fromIndex + (fromRight ? 1 : -1);
+  const length = array.length;
+  let index = fromIndex + (fromRight ? 1 : -1);
 
   while ((fromRight ? index-- : ++index < length)) {
     if (predicate(array[index], index, array)) {
diff --git a/_baseFlatten.js b/_baseFlatten.js
index b42dee6b9..1330b6d4e 100644
--- a/_baseFlatten.js
+++ b/_baseFlatten.js
@@ -13,14 +13,14 @@ import isFlattenable from './_isFlattenable.js';
  * @returns {Array} Returns the new flattened array.
  */
 function baseFlatten(array, depth, predicate, isStrict, result) {
-  var index = -1,
-      length = array.length;
+  let index = -1;
+  const length = array.length;
 
   predicate || (predicate = isFlattenable);
   result || (result = []);
 
   while (++index < length) {
-    var value = array[index];
+    const value = array[index];
     if (depth > 0 && predicate(value)) {
       if (depth > 1) {
         // Recursively flatten arrays (susceptible to call stack limits).
diff --git a/_baseFor.js b/_baseFor.js
index debbcf8cb..c8e080e01 100644
--- a/_baseFor.js
+++ b/_baseFor.js
@@ -11,6 +11,6 @@ import createBaseFor from './_createBaseFor.js';
  * @param {Function} keysFunc The function to get the keys of `object`.
  * @returns {Object} Returns `object`.
  */
-var baseFor = createBaseFor();
+const baseFor = createBaseFor();
 
 export default baseFor;
diff --git a/_baseForRight.js b/_baseForRight.js
index 85596da28..838f7f6c0 100644
--- a/_baseForRight.js
+++ b/_baseForRight.js
@@ -10,6 +10,6 @@ import createBaseFor from './_createBaseFor.js';
  * @param {Function} keysFunc The function to get the keys of `object`.
  * @returns {Object} Returns `object`.
  */
-var baseForRight = createBaseFor(true);
+const baseForRight = createBaseFor(true);
 
 export default baseForRight;
diff --git a/_baseGet.js b/_baseGet.js
index 16a2912ac..75e1ab06b 100644
--- a/_baseGet.js
+++ b/_baseGet.js
@@ -12,8 +12,8 @@ import toKey from './_toKey.js';
 function baseGet(object, path) {
   path = castPath(path, object);
 
-  var index = 0,
-      length = path.length;
+  let index = 0;
+  const length = path.length;
 
   while (object != null && index < length) {
     object = object[toKey(path[index++])];
diff --git a/_baseGetAllKeys.js b/_baseGetAllKeys.js
index af5533b09..16d8f4a85 100644
--- a/_baseGetAllKeys.js
+++ b/_baseGetAllKeys.js
@@ -13,7 +13,7 @@ import isArray from './isArray.js';
  * @returns {Array} Returns the array of property names and symbols.
  */
 function baseGetAllKeys(object, keysFunc, symbolsFunc) {
-  var result = keysFunc(object);
+  const result = keysFunc(object);
   return isArray(object) ? result : arrayPush(result, symbolsFunc(object));
 }
 
diff --git a/_baseGetTag.js b/_baseGetTag.js
index 61b440a06..4dc4df2a7 100644
--- a/_baseGetTag.js
+++ b/_baseGetTag.js
@@ -3,11 +3,11 @@ import getRawTag from './_getRawTag.js';
 import objectToString from './_objectToString.js';
 
 /** `Object#toString` result references. */
-var nullTag = '[object Null]',
-    undefinedTag = '[object Undefined]';
+const nullTag = '[object Null]';
+const undefinedTag = '[object Undefined]';
 
 /** Built-in value references. */
-var symToStringTag = Symbol ? Symbol.toStringTag : undefined;
+const symToStringTag = Symbol ? Symbol.toStringTag : undefined;
 
 /**
  * The base implementation of `getTag` without fallbacks for buggy environments.
diff --git a/_baseHas.js b/_baseHas.js
index edbbe5feb..6838b7bcc 100644
--- a/_baseHas.js
+++ b/_baseHas.js
@@ -1,8 +1,8 @@
 /** Used for built-in method references. */
-var objectProto = Object.prototype;
+const objectProto = Object.prototype;
 
 /** Used to check objects for own properties. */
-var hasOwnProperty = objectProto.hasOwnProperty;
+const hasOwnProperty = objectProto.hasOwnProperty;
 
 /**
  * The base implementation of `_.has` without support for deep paths.
diff --git a/_baseInRange.js b/_baseInRange.js
index 4b249a55b..1b11989bf 100644
--- a/_baseInRange.js
+++ b/_baseInRange.js
@@ -1,6 +1,6 @@
 /* Built-in method references for those with the same name as other `lodash` methods. */
-var nativeMax = Math.max,
-    nativeMin = Math.min;
+const nativeMax = Math.max;
+const nativeMin = Math.min;
 
 /**
  * The base implementation of `_.inRange` which doesn't coerce arguments.
diff --git a/_baseIndexOfWith.js b/_baseIndexOfWith.js
index 38831b26b..f1a2206d8 100644
--- a/_baseIndexOfWith.js
+++ b/_baseIndexOfWith.js
@@ -9,8 +9,8 @@
  * @returns {number} Returns the index of the matched value, else `-1`.
  */
 function baseIndexOfWith(array, value, fromIndex, comparator) {
-  var index = fromIndex - 1,
-      length = array.length;
+  let index = fromIndex - 1;
+  const length = array.length;
 
   while (++index < length) {
     if (comparator(array[index], value)) {
diff --git a/_baseInvoke.js b/_baseInvoke.js
index e465d8460..48a1c5bb4 100644
--- a/_baseInvoke.js
+++ b/_baseInvoke.js
@@ -17,7 +17,7 @@ import toKey from './_toKey.js';
 function baseInvoke(object, path, args) {
   path = castPath(path, object);
   object = parent(object, path);
-  var func = object == null ? object : object[toKey(last(path))];
+  const func = object == null ? object : object[toKey(last(path))];
   return func == null ? undefined : apply(func, object, args);
 }
 
diff --git a/_baseIsArguments.js b/_baseIsArguments.js
index cbf4ca686..7116586f0 100644
--- a/_baseIsArguments.js
+++ b/_baseIsArguments.js
@@ -2,7 +2,7 @@ import baseGetTag from './_baseGetTag.js';
 import isObjectLike from './isObjectLike.js';
 
 /** `Object#toString` result references. */
-var argsTag = '[object Arguments]';
+const argsTag = '[object Arguments]';
 
 /**
  * The base implementation of `_.isArguments`.
diff --git a/_baseIsArrayBuffer.js b/_baseIsArrayBuffer.js
index 7a25a8f61..248536240 100644
--- a/_baseIsArrayBuffer.js
+++ b/_baseIsArrayBuffer.js
@@ -1,7 +1,7 @@
 import baseGetTag from './_baseGetTag.js';
 import isObjectLike from './isObjectLike.js';
 
-var arrayBufferTag = '[object ArrayBuffer]';
+const arrayBufferTag = '[object ArrayBuffer]';
 
 /**
  * The base implementation of `_.isArrayBuffer` without Node.js optimizations.
diff --git a/_baseIsDate.js b/_baseIsDate.js
index 5487cb51b..ce5883296 100644
--- a/_baseIsDate.js
+++ b/_baseIsDate.js
@@ -2,7 +2,7 @@ import baseGetTag from './_baseGetTag.js';
 import isObjectLike from './isObjectLike.js';
 
 /** `Object#toString` result references. */
-var dateTag = '[object Date]';
+const dateTag = '[object Date]';
 
 /**
  * The base implementation of `_.isDate` without Node.js optimizations.
diff --git a/_baseIsMap.js b/_baseIsMap.js
index 6438d2b03..87ff3f36d 100644
--- a/_baseIsMap.js
+++ b/_baseIsMap.js
@@ -2,7 +2,7 @@ import getTag from './_getTag.js';
 import isObjectLike from './isObjectLike.js';
 
 /** `Object#toString` result references. */
-var mapTag = '[object Map]';
+const mapTag = '[object Map]';
 
 /**
  * The base implementation of `_.isMap` without Node.js optimizations.
diff --git a/_baseIsRegExp.js b/_baseIsRegExp.js
index e73971b39..2a8f21f85 100644
--- a/_baseIsRegExp.js
+++ b/_baseIsRegExp.js
@@ -2,7 +2,7 @@ import baseGetTag from './_baseGetTag.js';
 import isObjectLike from './isObjectLike.js';
 
 /** `Object#toString` result references. */
-var regexpTag = '[object RegExp]';
+const regexpTag = '[object RegExp]';
 
 /**
  * The base implementation of `_.isRegExp` without Node.js optimizations.
diff --git a/_baseIsSet.js b/_baseIsSet.js
index bee4a8e4b..4e953b30c 100644
--- a/_baseIsSet.js
+++ b/_baseIsSet.js
@@ -2,7 +2,7 @@ import getTag from './_getTag.js';
 import isObjectLike from './isObjectLike.js';
 
 /** `Object#toString` result references. */
-var setTag = '[object Set]';
+const setTag = '[object Set]';
 
 /**
  * The base implementation of `_.isSet` without Node.js optimizations.
diff --git a/_baseKeys.js b/_baseKeys.js
index 5a7622490..8d71d6c6d 100644
--- a/_baseKeys.js
+++ b/_baseKeys.js
@@ -2,10 +2,10 @@ import isPrototype from './_isPrototype.js';
 import nativeKeys from './_nativeKeys.js';
 
 /** Used for built-in method references. */
-var objectProto = Object.prototype;
+const objectProto = Object.prototype;
 
 /** Used to check objects for own properties. */
-var hasOwnProperty = objectProto.hasOwnProperty;
+const hasOwnProperty = objectProto.hasOwnProperty;
 
 /**
  * The base implementation of `_.keys` which doesn't treat sparse arrays as dense.
@@ -18,8 +18,8 @@ function baseKeys(object) {
   if (!isPrototype(object)) {
     return nativeKeys(object);
   }
-  var result = [];
-  for (var key in Object(object)) {
+  const result = [];
+  for (const key in Object(object)) {
     if (hasOwnProperty.call(object, key) && key != 'constructor') {
       result.push(key);
     }
diff --git a/_baseKeysIn.js b/_baseKeysIn.js
index 84c1395cf..f7bca0392 100644
--- a/_baseKeysIn.js
+++ b/_baseKeysIn.js
@@ -3,10 +3,10 @@ import isPrototype from './_isPrototype.js';
 import nativeKeysIn from './_nativeKeysIn.js';
 
 /** Used for built-in method references. */
-var objectProto = Object.prototype;
+const objectProto = Object.prototype;
 
 /** Used to check objects for own properties. */
-var hasOwnProperty = objectProto.hasOwnProperty;
+const hasOwnProperty = objectProto.hasOwnProperty;
 
 /**
  * The base implementation of `_.keysIn` which doesn't treat sparse arrays as dense.
@@ -19,10 +19,10 @@ function baseKeysIn(object) {
   if (!isObject(object)) {
     return nativeKeysIn(object);
   }
-  var isProto = isPrototype(object),
-      result = [];
+  const isProto = isPrototype(object);
+  const result = [];
 
-  for (var key in object) {
+  for (const key in object) {
     if (!(key == 'constructor' && (isProto || !hasOwnProperty.call(object, key)))) {
       result.push(key);
     }
diff --git a/_baseMatches.js b/_baseMatches.js
index a8b556fed..5486c11f2 100644
--- a/_baseMatches.js
+++ b/_baseMatches.js
@@ -10,7 +10,7 @@ import matchesStrictComparable from './_matchesStrictComparable.js';
  * @returns {Function} Returns the new spec function.
  */
 function baseMatches(source) {
-  var matchData = getMatchData(source);
+  const matchData = getMatchData(source);
   if (matchData.length == 1 && matchData[0][2]) {
     return matchesStrictComparable(matchData[0][0], matchData[0][1]);
   }
diff --git a/_baseMatchesProperty.js b/_baseMatchesProperty.js
index 6370abd5a..f6e6b36dc 100644
--- a/_baseMatchesProperty.js
+++ b/_baseMatchesProperty.js
@@ -7,8 +7,8 @@ import matchesStrictComparable from './_matchesStrictComparable.js';
 import toKey from './_toKey.js';
 
 /** Used to compose bitmasks for value comparisons. */
-var COMPARE_PARTIAL_FLAG = 1,
-    COMPARE_UNORDERED_FLAG = 2;
+const COMPARE_PARTIAL_FLAG = 1;
+const COMPARE_UNORDERED_FLAG = 2;
 
 /**
  * The base implementation of `_.matchesProperty` which doesn't clone `srcValue`.
@@ -23,7 +23,7 @@ function baseMatchesProperty(path, srcValue) {
     return matchesStrictComparable(toKey(path), srcValue);
   }
   return object => {
-    var objValue = get(object, path);
+    const objValue = get(object, path);
     return (objValue === undefined && objValue === srcValue)
       ? hasIn(object, path)
       : baseIsEqual(srcValue, objValue, COMPARE_PARTIAL_FLAG | COMPARE_UNORDERED_FLAG);
diff --git a/_baseMean.js b/_baseMean.js
index f2f1c57fb..c87baec2c 100644
--- a/_baseMean.js
+++ b/_baseMean.js
@@ -1,7 +1,7 @@
 import baseSum from './_baseSum.js';
 
 /** Used as references for various `Number` constants. */
-var NAN = 0 / 0;
+const NAN = 0 / 0;
 
 /**
  * The base implementation of `_.mean` and `_.meanBy` without support for
@@ -13,7 +13,7 @@ var NAN = 0 / 0;
  * @returns {number} Returns the mean.
  */
 function baseMean(array, iteratee) {
-  var length = array == null ? 0 : array.length;
+  const length = array == null ? 0 : array.length;
   return length ? (baseSum(array, iteratee) / length) : NAN;
 }
 
diff --git a/_baseNth.js b/_baseNth.js
index 0a6e9998b..c4f5bde4c 100644
--- a/_baseNth.js
+++ b/_baseNth.js
@@ -9,7 +9,7 @@ import isIndex from './_isIndex.js';
  * @returns {*} Returns the nth element of `array`.
  */
 function baseNth(array, n) {
-  var length = array.length;
+  const length = array.length;
   if (!length) {
     return;
   }
diff --git a/_baseOrderBy.js b/_baseOrderBy.js
index bc8a47e64..641599472 100644
--- a/_baseOrderBy.js
+++ b/_baseOrderBy.js
@@ -16,11 +16,11 @@ import identity from './identity.js';
  * @returns {Array} Returns the new sorted array.
  */
 function baseOrderBy(collection, iteratees, orders) {
-  var index = -1;
+  let index = -1;
   iteratees = arrayMap(iteratees.length ? iteratees : [identity], baseUnary(baseIteratee));
 
-  var result = baseMap(collection, (value, key, collection) => {
-    var criteria = arrayMap(iteratees, iteratee => iteratee(value));
+  const result = baseMap(collection, (value, key, collection) => {
+    const criteria = arrayMap(iteratees, iteratee => iteratee(value));
     return { 'criteria': criteria, 'index': ++index, 'value': value };
   });
 
diff --git a/_basePullAt.js b/_basePullAt.js
index 9305613ed..ace3465f6 100644
--- a/_basePullAt.js
+++ b/_basePullAt.js
@@ -2,10 +2,10 @@ import baseUnset from './_baseUnset.js';
 import isIndex from './_isIndex.js';
 
 /** Used for built-in method references. */
-var arrayProto = Array.prototype;
+const arrayProto = Array.prototype;
 
 /** Built-in value references. */
-var splice = arrayProto.splice;
+const splice = arrayProto.splice;
 
 /**
  * The base implementation of `_.pullAt` without support for individual
@@ -17,11 +17,11 @@ var splice = arrayProto.splice;
  * @returns {Array} Returns `array`.
  */
 function basePullAt(array, indexes) {
-  var length = array ? indexes.length : 0,
-      lastIndex = length - 1;
+  let length = array ? indexes.length : 0;
+  const lastIndex = length - 1;
 
   while (length--) {
-    var index = indexes[length];
+    const index = indexes[length];
     if (length == lastIndex || index !== previous) {
       var previous = index;
       if (isIndex(index)) {
diff --git a/_baseRepeat.js b/_baseRepeat.js
index 594539a7a..5e7c35a6d 100644
--- a/_baseRepeat.js
+++ b/_baseRepeat.js
@@ -1,8 +1,8 @@
 /** Used as references for various `Number` constants. */
-var MAX_SAFE_INTEGER = 9007199254740991;
+const MAX_SAFE_INTEGER = 9007199254740991;
 
 /* Built-in method references for those with the same name as other `lodash` methods. */
-var nativeFloor = Math.floor;
+const nativeFloor = Math.floor;
 
 /**
  * The base implementation of `_.repeat` which doesn't coerce arguments.
@@ -13,7 +13,7 @@ var nativeFloor = Math.floor;
  * @returns {string} Returns the repeated string.
  */
 function baseRepeat(string, n) {
-  var result = '';
+  let result = '';
   if (!string || n < 1 || n > MAX_SAFE_INTEGER) {
     return result;
   }
diff --git a/_baseSampleSize.js b/_baseSampleSize.js
index 04877a16b..c693c6f5a 100644
--- a/_baseSampleSize.js
+++ b/_baseSampleSize.js
@@ -11,7 +11,7 @@ import values from './values.js';
  * @returns {Array} Returns the random elements.
  */
 function baseSampleSize(collection, n) {
-  var array = values(collection);
+  const array = values(collection);
   return shuffleSelf(array, baseClamp(n, 0, array.length));
 }
 
diff --git a/_baseSetData.js b/_baseSetData.js
index f901afef2..fc36f3bed 100644
--- a/_baseSetData.js
+++ b/_baseSetData.js
@@ -9,7 +9,7 @@ import metaMap from './_metaMap.js';
  * @param {*} data The metadata.
  * @returns {Function} Returns `func`.
  */
-var baseSetData = !metaMap ? identity : (func, data) => {
+const baseSetData = !metaMap ? identity : (func, data) => {
   metaMap.set(func, data);
   return func;
 };
diff --git a/_baseSetToString.js b/_baseSetToString.js
index 2a00fceff..d2bed4b79 100644
--- a/_baseSetToString.js
+++ b/_baseSetToString.js
@@ -10,7 +10,7 @@ import identity from './identity.js';
  * @param {Function} string The `toString` result.
  * @returns {Function} Returns `func`.
  */
-var baseSetToString = !defineProperty ? identity : (func, string) => defineProperty(func, 'toString', {
+const baseSetToString = !defineProperty ? identity : (func, string) => defineProperty(func, 'toString', {
   'configurable': true,
   'enumerable': false,
   'value': constant(string),
diff --git a/_baseSome.js b/_baseSome.js
index aec0ff733..7db1a7b6d 100644
--- a/_baseSome.js
+++ b/_baseSome.js
@@ -10,7 +10,7 @@ import baseEach from './_baseEach.js';
  *  else `false`.
  */
 function baseSome(collection, predicate) {
-  var result;
+  let result;
 
   baseEach(collection, (value, index, collection) => {
     result = predicate(value, index, collection);
diff --git a/_baseSortBy.js b/_baseSortBy.js
index e2041cd66..682bc88fa 100644
--- a/_baseSortBy.js
+++ b/_baseSortBy.js
@@ -9,7 +9,7 @@
  * @returns {Array} Returns `array`.
  */
 function baseSortBy(array, comparer) {
-  var length = array.length;
+  let length = array.length;
 
   array.sort(comparer);
   while (length--) {
diff --git a/_baseSum.js b/_baseSum.js
index 61b3da44f..9d79920f7 100644
--- a/_baseSum.js
+++ b/_baseSum.js
@@ -8,12 +8,12 @@
  * @returns {number} Returns the sum.
  */
 function baseSum(array, iteratee) {
-  var result,
-      index = -1,
-      length = array.length;
+  let result;
+  let index = -1;
+  const length = array.length;
 
   while (++index < length) {
-    var current = iteratee(array[index]);
+    const current = iteratee(array[index]);
     if (current !== undefined) {
       result = result === undefined ? current : (result + current);
     }
diff --git a/_baseTimes.js b/_baseTimes.js
index d5d0e274f..e4954747e 100644
--- a/_baseTimes.js
+++ b/_baseTimes.js
@@ -8,8 +8,8 @@
  * @returns {Array} Returns the array of results.
  */
 function baseTimes(n, iteratee) {
-  var index = -1,
-      result = Array(n);
+  let index = -1;
+  const result = Array(n);
 
   while (++index < n) {
     result[index] = iteratee(index);
diff --git a/_baseToNumber.js b/_baseToNumber.js
index 3552d1a21..167108ef5 100644
--- a/_baseToNumber.js
+++ b/_baseToNumber.js
@@ -1,7 +1,7 @@
 import isSymbol from './isSymbol.js';
 
 /** Used as references for various `Number` constants. */
-var NAN = 0 / 0;
+const NAN = 0 / 0;
 
 /**
  * The base implementation of `_.toNumber` which doesn't ensure correct
diff --git a/_baseWhile.js b/_baseWhile.js
index 5536ea6ef..d9fbe0c4a 100644
--- a/_baseWhile.js
+++ b/_baseWhile.js
@@ -12,8 +12,8 @@ import baseSlice from './_baseSlice.js';
  * @returns {Array} Returns the slice of `array`.
  */
 function baseWhile(array, predicate, isDrop, fromRight) {
-  var length = array.length,
-      index = fromRight ? length : -1;
+  const length = array.length;
+  let index = fromRight ? length : -1;
 
   while ((fromRight ? index-- : ++index < length) &&
     predicate(array[index], index, array)) {}
diff --git a/_baseWrapperValue.js b/_baseWrapperValue.js
index 3e6990ad8..f264820b1 100644
--- a/_baseWrapperValue.js
+++ b/_baseWrapperValue.js
@@ -13,7 +13,7 @@ import arrayReduce from './_arrayReduce.js';
  * @returns {*} Returns the resolved value.
  */
 function baseWrapperValue(value, actions) {
-  var result = value;
+  let result = value;
   if (result instanceof LazyWrapper) {
     result = result.value();
   }
diff --git a/_baseXor.js b/_baseXor.js
index 9cebe6748..8509f3807 100644
--- a/_baseXor.js
+++ b/_baseXor.js
@@ -13,16 +13,16 @@ import baseUniq from './_baseUniq.js';
  * @returns {Array} Returns the new array of values.
  */
 function baseXor(arrays, iteratee, comparator) {
-  var length = arrays.length;
+  const length = arrays.length;
   if (length < 2) {
     return length ? baseUniq(arrays[0]) : [];
   }
-  var index = -1,
-      result = Array(length);
+  let index = -1;
+  const result = Array(length);
 
   while (++index < length) {
-    var array = arrays[index],
-        othIndex = -1;
+    const array = arrays[index];
+    let othIndex = -1;
 
     while (++othIndex < length) {
       if (othIndex != index) {
diff --git a/_baseZipObject.js b/_baseZipObject.js
index f6f4a3cc5..e3f840ac6 100644
--- a/_baseZipObject.js
+++ b/_baseZipObject.js
@@ -8,13 +8,13 @@
  * @returns {Object} Returns the new object.
  */
 function baseZipObject(props, values, assignFunc) {
-  var index = -1,
-      length = props.length,
-      valsLength = values.length,
-      result = {};
+  let index = -1;
+  const length = props.length;
+  const valsLength = values.length;
+  const result = {};
 
   while (++index < length) {
-    var value = index < valsLength ? values[index] : undefined;
+    const value = index < valsLength ? values[index] : undefined;
     assignFunc(result, props[index], value);
   }
   return result;
diff --git a/_castRest.js b/_castRest.js
index 6f43d021a..e8e7ddf53 100644
--- a/_castRest.js
+++ b/_castRest.js
@@ -9,6 +9,6 @@ import baseRest from './_baseRest.js';
  * @param {Function} func The function to apply a rest parameter to.
  * @returns {Function} Returns the new function.
  */
-var castRest = baseRest;
+const castRest = baseRest;
 
 export default castRest;
diff --git a/_castSlice.js b/_castSlice.js
index 011bbe4eb..9e906fb9c 100644
--- a/_castSlice.js
+++ b/_castSlice.js
@@ -10,7 +10,7 @@ import baseSlice from './_baseSlice.js';
  * @returns {Array} Returns the cast slice.
  */
 function castSlice(array, start, end) {
-  var length = array.length;
+  const length = array.length;
   end = end === undefined ? length : end;
   return (!start && end >= length) ? array : baseSlice(array, start, end);
 }
diff --git a/_charsEndIndex.js b/_charsEndIndex.js
index af9926e7a..92ba6411a 100644
--- a/_charsEndIndex.js
+++ b/_charsEndIndex.js
@@ -10,7 +10,7 @@ import baseIndexOf from './_baseIndexOf.js';
  * @returns {number} Returns the index of the last unmatched string symbol.
  */
 function charsEndIndex(strSymbols, chrSymbols) {
-  var index = strSymbols.length;
+  let index = strSymbols.length;
 
   while (index-- && baseIndexOf(chrSymbols, strSymbols[index], 0) > -1) {}
   return index;
diff --git a/_charsStartIndex.js b/_charsStartIndex.js
index 7406b19f4..25018d28b 100644
--- a/_charsStartIndex.js
+++ b/_charsStartIndex.js
@@ -10,11 +10,11 @@ import baseIndexOf from './_baseIndexOf.js';
  * @returns {number} Returns the index of the first unmatched string symbol.
  */
 function charsStartIndex(strSymbols, chrSymbols) {
-  var index = -1,
-      length = strSymbols.length;
+ let index = -1;
+ const length = strSymbols.length;
 
-  while (++index < length && baseIndexOf(chrSymbols, strSymbols[index], 0) > -1) {}
-  return index;
+ while (++index < length && baseIndexOf(chrSymbols, strSymbols[index], 0) > -1) {}
+ return index;
 }
 
 export default charsStartIndex;
diff --git a/_cloneArrayBuffer.js b/_cloneArrayBuffer.js
index 9f33e7a7c..2c8cb0fae 100644
--- a/_cloneArrayBuffer.js
+++ b/_cloneArrayBuffer.js
@@ -8,7 +8,7 @@ import Uint8Array from './_Uint8Array.js';
  * @returns {ArrayBuffer} Returns the cloned array buffer.
  */
 function cloneArrayBuffer(arrayBuffer) {
-  var result = new arrayBuffer.constructor(arrayBuffer.byteLength);
+  const result = new arrayBuffer.constructor(arrayBuffer.byteLength);
   new Uint8Array(result).set(new Uint8Array(arrayBuffer));
   return result;
 }
diff --git a/_cloneDataView.js b/_cloneDataView.js
index f9b9a6f03..c7294e03a 100644
--- a/_cloneDataView.js
+++ b/_cloneDataView.js
@@ -9,7 +9,7 @@ import cloneArrayBuffer from './_cloneArrayBuffer.js';
  * @returns {Object} Returns the cloned data view.
  */
 function cloneDataView(dataView, isDeep) {
-  var buffer = isDeep ? cloneArrayBuffer(dataView.buffer) : dataView.buffer;
+  const buffer = isDeep ? cloneArrayBuffer(dataView.buffer) : dataView.buffer;
   return new dataView.constructor(buffer, dataView.byteOffset, dataView.byteLength);
 }
 
diff --git a/_cloneMap.js b/_cloneMap.js
index a4aa5b5d6..31f27a368 100644
--- a/_cloneMap.js
+++ b/_cloneMap.js
@@ -3,7 +3,7 @@ import arrayReduce from './_arrayReduce.js';
 import mapToArray from './_mapToArray.js';
 
 /** Used to compose bitmasks for cloning. */
-var CLONE_DEEP_FLAG = 1;
+const CLONE_DEEP_FLAG = 1;
 
 /**
  * Creates a clone of `map`.
@@ -15,7 +15,7 @@ var CLONE_DEEP_FLAG = 1;
  * @returns {Object} Returns the cloned map.
  */
 function cloneMap(map, isDeep, cloneFunc) {
-  var array = isDeep ? cloneFunc(mapToArray(map), CLONE_DEEP_FLAG) : mapToArray(map);
+  const array = isDeep ? cloneFunc(mapToArray(map), CLONE_DEEP_FLAG) : mapToArray(map);
   return arrayReduce(array, addMapEntry, new map.constructor);
 }
 
diff --git a/_cloneRegExp.js b/_cloneRegExp.js
index 0ddb49b4c..1616a124c 100644
--- a/_cloneRegExp.js
+++ b/_cloneRegExp.js
@@ -1,5 +1,5 @@
 /** Used to match `RegExp` flags from their coerced string values. */
-var reFlags = /\w*$/;
+const reFlags = /\w*$/;
 
 /**
  * Creates a clone of `regexp`.
@@ -9,7 +9,7 @@ var reFlags = /\w*$/;
  * @returns {Object} Returns the cloned regexp.
  */
 function cloneRegExp(regexp) {
-  var result = new regexp.constructor(regexp.source, reFlags.exec(regexp));
+  const result = new regexp.constructor(regexp.source, reFlags.exec(regexp));
   result.lastIndex = regexp.lastIndex;
   return result;
 }
diff --git a/_cloneSet.js b/_cloneSet.js
index e1d1063d0..361c55d27 100644
--- a/_cloneSet.js
+++ b/_cloneSet.js
@@ -3,7 +3,7 @@ import arrayReduce from './_arrayReduce.js';
 import setToArray from './_setToArray.js';
 
 /** Used to compose bitmasks for cloning. */
-var CLONE_DEEP_FLAG = 1;
+const CLONE_DEEP_FLAG = 1;
 
 /**
  * Creates a clone of `set`.
@@ -15,7 +15,7 @@ var CLONE_DEEP_FLAG = 1;
  * @returns {Object} Returns the cloned set.
  */
 function cloneSet(set, isDeep, cloneFunc) {
-  var array = isDeep ? cloneFunc(setToArray(set), CLONE_DEEP_FLAG) : setToArray(set);
+  const array = isDeep ? cloneFunc(setToArray(set), CLONE_DEEP_FLAG) : setToArray(set);
   return arrayReduce(array, addSetEntry, new set.constructor);
 }
 
diff --git a/_cloneTypedArray.js b/_cloneTypedArray.js
index 2fa9b8a6a..8f962fc15 100644
--- a/_cloneTypedArray.js
+++ b/_cloneTypedArray.js
@@ -9,7 +9,7 @@ import cloneArrayBuffer from './_cloneArrayBuffer.js';
  * @returns {Object} Returns the cloned typed array.
  */
 function cloneTypedArray(typedArray, isDeep) {
-  var buffer = isDeep ? cloneArrayBuffer(typedArray.buffer) : typedArray.buffer;
+  const buffer = isDeep ? cloneArrayBuffer(typedArray.buffer) : typedArray.buffer;
   return new typedArray.constructor(buffer, typedArray.byteOffset, typedArray.length);
 }
 
diff --git a/_copyArray.js b/_copyArray.js
index b29b71e95..7968f3787 100644
--- a/_copyArray.js
+++ b/_copyArray.js
@@ -7,8 +7,8 @@
  * @returns {Array} Returns `array`.
  */
 function copyArray(source, array) {
-  var index = -1,
-      length = source.length;
+  let index = -1;
+  const length = source.length;
 
   array || (array = Array(length));
   while (++index < length) {
diff --git a/_copyObject.js b/_copyObject.js
index 4e2475553..1f83892b4 100644
--- a/_copyObject.js
+++ b/_copyObject.js
@@ -12,16 +12,16 @@ import baseAssignValue from './_baseAssignValue.js';
  * @returns {Object} Returns `object`.
  */
 function copyObject(source, props, object, customizer) {
-  var isNew = !object;
+  const isNew = !object;
   object || (object = {});
 
-  var index = -1,
-      length = props.length;
+  let index = -1;
+  const length = props.length;
 
   while (++index < length) {
-    var key = props[index];
+    const key = props[index];
 
-    var newValue = customizer
+    let newValue = customizer
       ? customizer(object[key], source[key], key, object, source)
       : undefined;
 
diff --git a/_coreJsData.js b/_coreJsData.js
index 2ad4fc142..7e944be80 100644
--- a/_coreJsData.js
+++ b/_coreJsData.js
@@ -1,6 +1,6 @@
 import root from './_root.js';
 
 /** Used to detect overreaching core-js shims. */
-var coreJsData = root['__core-js_shared__'];
+const coreJsData = root['__core-js_shared__'];
 
 export default coreJsData;
diff --git a/_createBaseEach.js b/_createBaseEach.js
index 94f6fa28a..96ccda7fb 100644
--- a/_createBaseEach.js
+++ b/_createBaseEach.js
@@ -16,9 +16,9 @@ function createBaseEach(eachFunc, fromRight) {
     if (!isArrayLike(collection)) {
       return eachFunc(collection, iteratee);
     }
-    var length = collection.length,
-        index = fromRight ? length : -1,
-        iterable = Object(collection);
+    const length = collection.length;
+    const iterable = Object(collection);
+    let index = fromRight ? length : -1;
 
     while ((fromRight ? index-- : ++index < length)) {
       if (iteratee(iterable[index], index, iterable) === false) {
diff --git a/_createCaseFirst.js b/_createCaseFirst.js
index 83847c576..43af01d52 100644
--- a/_createCaseFirst.js
+++ b/_createCaseFirst.js
@@ -14,15 +14,15 @@ function createCaseFirst(methodName) {
   return string => {
     string = toString(string);
 
-    var strSymbols = hasUnicode(string)
+    const strSymbols = hasUnicode(string)
       ? stringToArray(string)
       : undefined;
 
-    var chr = strSymbols
+    const chr = strSymbols
       ? strSymbols[0]
       : string.charAt(0);
 
-    var trailing = strSymbols
+    const trailing = strSymbols
       ? castSlice(strSymbols, 1).join('')
       : string.slice(1);
 
diff --git a/_createCompounder.js b/_createCompounder.js
index a64ce89e4..5154f58a4 100644
--- a/_createCompounder.js
+++ b/_createCompounder.js
@@ -3,10 +3,10 @@ import deburr from './deburr.js';
 import words from './words.js';
 
 /** Used to compose unicode capture groups. */
-var rsApos = "['\u2019]";
+const rsApos = "['\u2019]";
 
 /** Used to match apostrophes. */
-var reApos = RegExp(rsApos, 'g');
+const reApos = RegExp(rsApos, 'g');
 
 /**
  * Creates a function like `_.camelCase`.
diff --git a/_createFind.js b/_createFind.js
index a6f6c2169..94a5fbd43 100644
--- a/_createFind.js
+++ b/_createFind.js
@@ -11,13 +11,13 @@ import keys from './keys.js';
  */
 function createFind(findIndexFunc) {
   return (collection, predicate, fromIndex) => {
-    var iterable = Object(collection);
+    const iterable = Object(collection);
     if (!isArrayLike(collection)) {
       var iteratee = baseIteratee(predicate, 3);
       collection = keys(collection);
       predicate = key => iteratee(iterable[key], key, iterable);
     }
-    var index = findIndexFunc(collection, predicate, fromIndex);
+    const index = findIndexFunc(collection, predicate, fromIndex);
     return index > -1 ? iterable[iteratee ? collection[index] : index] : undefined;
   };
 }
diff --git a/_createMathOperation.js b/_createMathOperation.js
index fd26eb2e2..4b46b7d1c 100644
--- a/_createMathOperation.js
+++ b/_createMathOperation.js
@@ -11,7 +11,7 @@ import baseToString from './_baseToString.js';
  */
 function createMathOperation(operator, defaultValue) {
   return (value, other) => {
-    var result;
+    let result;
     if (value === undefined && other === undefined) {
       return defaultValue;
     }
diff --git a/_createOver.js b/_createOver.js
index 68d67cc3f..4093c5fd6 100644
--- a/_createOver.js
+++ b/_createOver.js
@@ -16,7 +16,7 @@ function createOver(arrayFunc) {
   return flatRest(iteratees => {
     iteratees = arrayMap(iteratees, baseUnary(baseIteratee));
     return baseRest(function(args) {
-      var thisArg = this;
+      const thisArg = this;
       return arrayFunc(iteratees, iteratee => apply(iteratee, thisArg, args));
     });
   });
diff --git a/_createPadding.js b/_createPadding.js
index 1e35cd82b..fd118122b 100644
--- a/_createPadding.js
+++ b/_createPadding.js
@@ -6,7 +6,7 @@ import stringSize from './_stringSize.js';
 import stringToArray from './_stringToArray.js';
 
 /* Built-in method references for those with the same name as other `lodash` methods. */
-var nativeCeil = Math.ceil;
+const nativeCeil = Math.ceil;
 
 /**
  * Creates the padding for `string` based on `length`. The `chars` string
@@ -20,11 +20,11 @@ var nativeCeil = Math.ceil;
 function createPadding(length, chars) {
   chars = chars === undefined ? ' ' : baseToString(chars);
 
-  var charsLength = chars.length;
+  const charsLength = chars.length;
   if (charsLength < 2) {
     return charsLength ? baseRepeat(chars, length) : chars;
   }
-  var result = baseRepeat(chars, nativeCeil(length / stringSize(chars)));
+  const result = baseRepeat(chars, nativeCeil(length / stringSize(chars)));
   return hasUnicode(chars)
     ? castSlice(stringToArray(result), 0, length).join('')
     : result.slice(0, length);
diff --git a/_createSet.js b/_createSet.js
index 811d1109a..a103e0c28 100644
--- a/_createSet.js
+++ b/_createSet.js
@@ -3,7 +3,7 @@ import noop from './noop.js';
 import setToArray from './_setToArray.js';
 
 /** Used as references for various `Number` constants. */
-var INFINITY = 1 / 0;
+const INFINITY = 1 / 0;
 
 /**
  * Creates a set object of `values`.
@@ -12,6 +12,6 @@ var INFINITY = 1 / 0;
  * @param {Array} values The values to add to the set.
  * @returns {Object} Returns the new set.
  */
-var createSet = !(Set && (1 / setToArray(new Set([,-0]))[1]) == INFINITY) ? noop : values => new Set(values);
+const createSet = !(Set && (1 / setToArray(new Set([,-0]))[1]) == INFINITY) ? noop : values => new Set(values);
 
 export default createSet;
diff --git a/_customDefaultsAssignIn.js b/_customDefaultsAssignIn.js
index 0de9339b2..f15495f72 100644
--- a/_customDefaultsAssignIn.js
+++ b/_customDefaultsAssignIn.js
@@ -1,10 +1,10 @@
 import eq from './eq.js';
 
 /** Used for built-in method references. */
-var objectProto = Object.prototype;
+const objectProto = Object.prototype;
 
 /** Used to check objects for own properties. */
-var hasOwnProperty = objectProto.hasOwnProperty;
+const hasOwnProperty = objectProto.hasOwnProperty;
 
 /**
  * Used by `_.defaults` to customize its `_.assignIn` use to assign properties
diff --git a/_deburrLetter.js b/_deburrLetter.js
index 88a7b99df..b89e776e3 100644
--- a/_deburrLetter.js
+++ b/_deburrLetter.js
@@ -1,7 +1,7 @@
 import basePropertyOf from './_basePropertyOf.js';
 
 /** Used to map Latin Unicode letters to basic Latin letters. */
-var deburredLetters = {
+const deburredLetters = {
   // Latin-1 Supplement block.
   '\xc0': 'A',  '\xc1': 'A', '\xc2': 'A', '\xc3': 'A', '\xc4': 'A', '\xc5': 'A',
   '\xe0': 'a',  '\xe1': 'a', '\xe2': 'a', '\xe3': 'a', '\xe4': 'a', '\xe5': 'a',
@@ -66,6 +66,6 @@ var deburredLetters = {
  * @param {string} letter The matched letter to deburr.
  * @returns {string} Returns the deburred letter.
  */
-var deburrLetter = basePropertyOf(deburredLetters);
+const deburrLetter = basePropertyOf(deburredLetters);
 
 export default deburrLetter;
diff --git a/_defineProperty.js b/_defineProperty.js
index e94f8fa47..b2b07a94c 100644
--- a/_defineProperty.js
+++ b/_defineProperty.js
@@ -1,8 +1,8 @@
 import getNative from './_getNative.js';
 
-var defineProperty = ((() => {
+const defineProperty = ((() => {
   try {
-    var func = getNative(Object, 'defineProperty');
+    const func = getNative(Object, 'defineProperty');
     func({}, '', {});
     return func;
   } catch (e) {}
diff --git a/_escapeHtmlChar.js b/_escapeHtmlChar.js
index 536240335..ab600d1db 100644
--- a/_escapeHtmlChar.js
+++ b/_escapeHtmlChar.js
@@ -1,7 +1,7 @@
 import basePropertyOf from './_basePropertyOf.js';
 
 /** Used to map characters to HTML entities. */
-var htmlEscapes = {
+const htmlEscapes = {
   '&': '&amp;',
   '<': '&lt;',
   '>': '&gt;',
@@ -16,6 +16,6 @@ var htmlEscapes = {
  * @param {string} chr The matched character to escape.
  * @returns {string} Returns the escaped character.
  */
-var escapeHtmlChar = basePropertyOf(htmlEscapes);
+const escapeHtmlChar = basePropertyOf(htmlEscapes);
 
 export default escapeHtmlChar;
diff --git a/_escapeStringChar.js b/_escapeStringChar.js
index 164270a72..80f1b1a66 100644
--- a/_escapeStringChar.js
+++ b/_escapeStringChar.js
@@ -1,5 +1,5 @@
 /** Used to escape characters for inclusion in compiled string literals. */
-var stringEscapes = {
+const stringEscapes = {
   '\\': '\\',
   "'": "'",
   '\n': 'n',
diff --git a/_freeGlobal.js b/_freeGlobal.js
index 5e383a14c..a2e2e1735 100644
--- a/_freeGlobal.js
+++ b/_freeGlobal.js
@@ -1,4 +1,4 @@
 /** Detect free variable `global` from Node.js. */
-var freeGlobal = typeof global == 'object' && global && global.Object === Object && global;
+const freeGlobal = typeof global == 'object' && global && global.Object === Object && global;
 
 export default freeGlobal;
diff --git a/_getData.js b/_getData.js
index 237c60a9a..b27eb8706 100644
--- a/_getData.js
+++ b/_getData.js
@@ -8,6 +8,6 @@ import noop from './noop.js';
  * @param {Function} func The function to query.
  * @returns {*} Returns the metadata for `func`.
  */
-var getData = !metaMap ? noop : func => metaMap.get(func);
+const getData = !metaMap ? noop : func => metaMap.get(func);
 
 export default getData;
diff --git a/_getHolder.js b/_getHolder.js
index 9f76b190b..1e4ce3ecc 100644
--- a/_getHolder.js
+++ b/_getHolder.js
@@ -6,7 +6,7 @@
  * @returns {*} Returns the placeholder value.
  */
 function getHolder(func) {
-  var object = func;
+  const object = func;
   return object.placeholder;
 }
 
diff --git a/_getMapData.js b/_getMapData.js
index 7851b5403..6617cc2ce 100644
--- a/_getMapData.js
+++ b/_getMapData.js
@@ -9,7 +9,7 @@ import isKeyable from './_isKeyable.js';
  * @returns {*} Returns the map data.
  */
 function getMapData({ __data__ }, key) {
-  var data = __data__;
+  const data = __data__;
   return isKeyable(key)
     ? data[typeof key == 'string' ? 'string' : 'hash']
     : data.map;
diff --git a/_getNative.js b/_getNative.js
index d2cb43860..1a737ad9b 100644
--- a/_getNative.js
+++ b/_getNative.js
@@ -10,7 +10,7 @@ import getValue from './_getValue.js';
  * @returns {*} Returns the function if it's native, else `undefined`.
  */
 function getNative(object, key) {
-  var value = getValue(object, key);
+  const value = getValue(object, key);
   return baseIsNative(value) ? value : undefined;
 }
 
diff --git a/_getPrototype.js b/_getPrototype.js
index ce92d4885..04370e6ac 100644
--- a/_getPrototype.js
+++ b/_getPrototype.js
@@ -1,6 +1,6 @@
 import overArg from './_overArg.js';
 
 /** Built-in value references. */
-var getPrototype = overArg(Object.getPrototypeOf, Object);
+const getPrototype = overArg(Object.getPrototypeOf, Object);
 
 export default getPrototype;
diff --git a/_getSymbols.js b/_getSymbols.js
index 985337634..72687d3f6 100644
--- a/_getSymbols.js
+++ b/_getSymbols.js
@@ -2,13 +2,13 @@ import arrayFilter from './_arrayFilter.js';
 import stubArray from './stubArray.js';
 
 /** Used for built-in method references. */
-var objectProto = Object.prototype;
+const objectProto = Object.prototype;
 
 /** Built-in value references. */
-var propertyIsEnumerable = objectProto.propertyIsEnumerable;
+const propertyIsEnumerable = objectProto.propertyIsEnumerable;
 
 /* Built-in method references for those with the same name as other `lodash` methods. */
-var nativeGetSymbols = Object.getOwnPropertySymbols;
+const nativeGetSymbols = Object.getOwnPropertySymbols;
 
 /**
  * Creates an array of the own enumerable symbols of `object`.
@@ -17,7 +17,7 @@ var nativeGetSymbols = Object.getOwnPropertySymbols;
  * @param {Object} object The object to query.
  * @returns {Array} Returns the array of symbols.
  */
-var getSymbols = !nativeGetSymbols ? stubArray : object => {
+const getSymbols = !nativeGetSymbols ? stubArray : object => {
   if (object == null) {
     return [];
   }
diff --git a/_getSymbolsIn.js b/_getSymbolsIn.js
index 3e5dd4ef9..419906b2b 100644
--- a/_getSymbolsIn.js
+++ b/_getSymbolsIn.js
@@ -4,7 +4,7 @@ import getSymbols from './_getSymbols.js';
 import stubArray from './stubArray.js';
 
 /* Built-in method references for those with the same name as other `lodash` methods. */
-var nativeGetSymbols = Object.getOwnPropertySymbols;
+const nativeGetSymbols = Object.getOwnPropertySymbols;
 
 /**
  * Creates an array of the own and inherited enumerable symbols of `object`.
@@ -13,8 +13,8 @@ var nativeGetSymbols = Object.getOwnPropertySymbols;
  * @param {Object} object The object to query.
  * @returns {Array} Returns the array of symbols.
  */
-var getSymbolsIn = !nativeGetSymbols ? stubArray : object => {
-  var result = [];
+const getSymbolsIn = !nativeGetSymbols ? stubArray : object => {
+  const result = [];
   while (object) {
     arrayPush(result, getSymbols(object));
     object = getPrototype(object);
diff --git a/_hasPath.js b/_hasPath.js
index 7decc6c06..44c25d3fd 100644
--- a/_hasPath.js
+++ b/_hasPath.js
@@ -17,7 +17,7 @@ import toKey from './_toKey.js';
 function hasPath(object, path, hasFunc) {
   path = castPath(path, object);
 
-  var index = -1,
+  let index = -1,
       length = path.length,
       result = false;
 
diff --git a/_hashDelete.js b/_hashDelete.js
index 509839f51..863dc6d69 100644
--- a/_hashDelete.js
+++ b/_hashDelete.js
@@ -9,7 +9,7 @@
  * @returns {boolean} Returns `true` if the entry was removed, else `false`.
  */
 function hashDelete(key) {
-  var result = this.has(key) && delete this.__data__[key];
+  const result = this.has(key) && delete this.__data__[key];
   this.size -= result ? 1 : 0;
   return result;
 }
diff --git a/_hashGet.js b/_hashGet.js
index 4a3f43b27..14718d052 100644
--- a/_hashGet.js
+++ b/_hashGet.js
@@ -1,13 +1,13 @@
 import nativeCreate from './_nativeCreate.js';
 
 /** Used to stand-in for `undefined` hash values. */
-var HASH_UNDEFINED = '__lodash_hash_undefined__';
+const HASH_UNDEFINED = '__lodash_hash_undefined__';
 
 /** Used for built-in method references. */
-var objectProto = Object.prototype;
+const objectProto = Object.prototype;
 
 /** Used to check objects for own properties. */
-var hasOwnProperty = objectProto.hasOwnProperty;
+const hasOwnProperty = objectProto.hasOwnProperty;
 
 /**
  * Gets the hash value for `key`.
@@ -19,9 +19,9 @@ var hasOwnProperty = objectProto.hasOwnProperty;
  * @returns {*} Returns the entry value.
  */
 function hashGet(key) {
-  var data = this.__data__;
+  const data = this.__data__;
   if (nativeCreate) {
-    var result = data[key];
+    const result = data[key];
     return result === HASH_UNDEFINED ? undefined : result;
   }
   return hasOwnProperty.call(data, key) ? data[key] : undefined;
diff --git a/_hashHas.js b/_hashHas.js
index 6db025d8e..ba9c40703 100644
--- a/_hashHas.js
+++ b/_hashHas.js
@@ -1,10 +1,10 @@
 import nativeCreate from './_nativeCreate.js';
 
 /** Used for built-in method references. */
-var objectProto = Object.prototype;
+const objectProto = Object.prototype;
 
 /** Used to check objects for own properties. */
-var hasOwnProperty = objectProto.hasOwnProperty;
+const hasOwnProperty = objectProto.hasOwnProperty;
 
 /**
  * Checks if a hash value for `key` exists.
@@ -16,7 +16,7 @@ var hasOwnProperty = objectProto.hasOwnProperty;
  * @returns {boolean} Returns `true` if an entry for `key` exists, else `false`.
  */
 function hashHas(key) {
-  var data = this.__data__;
+  const data = this.__data__;
   return nativeCreate ? (data[key] !== undefined) : hasOwnProperty.call(data, key);
 }
 
diff --git a/_hashSet.js b/_hashSet.js
index 63a0115b0..3f7084008 100644
--- a/_hashSet.js
+++ b/_hashSet.js
@@ -1,7 +1,7 @@
 import nativeCreate from './_nativeCreate.js';
 
 /** Used to stand-in for `undefined` hash values. */
-var HASH_UNDEFINED = '__lodash_hash_undefined__';
+const HASH_UNDEFINED = '__lodash_hash_undefined__';
 
 /**
  * Sets the hash `key` to `value`.
@@ -14,7 +14,7 @@ var HASH_UNDEFINED = '__lodash_hash_undefined__';
  * @returns {Object} Returns the hash instance.
  */
 function hashSet(key, value) {
-  var data = this.__data__;
+  const data = this.__data__;
   this.size += this.has(key) ? 0 : 1;
   data[key] = (nativeCreate && value === undefined) ? HASH_UNDEFINED : value;
   return this;