diff --git a/commonjs/core.js b/commonjs/core.js
index 921d54f..16ee5bb 100644
--- a/commonjs/core.js
+++ b/commonjs/core.js
@@ -1,5 +1,4 @@
 Object.defineProperty(exports, "__esModule", { value: true });
-exports._areEquals = exports.validate = exports.validator = exports.applyReducer = exports.applyPatch = exports.applyOperation = exports.getValueByPointer = exports.deepClone = exports.JsonPatchError = void 0;
 var helpers_js_1 = require("./helpers.js");
 exports.JsonPatchError = helpers_js_1.PatchError;
 exports.deepClone = helpers_js_1._deepClone;
@@ -31,7 +30,7 @@ var objOps = {
         and is potentially unneeded */
         var removed = getValueByPointer(document, this.path);
         if (removed) {
-            removed = (0, helpers_js_1._deepClone)(removed);
+            removed = helpers_js_1._deepClone(removed);
         }
         var originalValue = applyOperation(document, { op: "remove", path: this.from }).removed;
         applyOperation(document, { op: "add", path: this.path, value: originalValue });
@@ -40,7 +39,7 @@ var objOps = {
     copy: function (obj, key, document) {
         var valueToCopy = getValueByPointer(document, this.from);
         // enforce copy by value so further operations don't affect source (see issue #177)
-        applyOperation(document, { op: "add", path: this.path, value: (0, helpers_js_1._deepClone)(valueToCopy) });
+        applyOperation(document, { op: "add", path: this.path, value: helpers_js_1._deepClone(valueToCopy) });
         return { newDocument: document };
     },
     test: function (obj, key, document) {
@@ -54,7 +53,7 @@ var objOps = {
 /* The operations applicable to an array. Many are the same as for the object */
 var arrOps = {
     add: function (arr, i, document) {
-        if ((0, helpers_js_1.isInteger)(i)) {
+        if (helpers_js_1.isInteger(i)) {
             arr.splice(i, 0, this.value);
         }
         else { // array props
@@ -168,7 +167,7 @@ function applyOperation(document, operation, validateOperation, mutateDocument,
     } /* END ROOT OPERATIONS */
     else {
         if (!mutateDocument) {
-            document = (0, helpers_js_1._deepClone)(document);
+            document = helpers_js_1._deepClone(document);
         }
         var path = operation.path || "";
         var keys = path.split('/');
@@ -187,7 +186,7 @@ function applyOperation(document, operation, validateOperation, mutateDocument,
         while (true) {
             key = keys[t];
             if (key && key.indexOf('~') != -1) {
-                key = (0, helpers_js_1.unescapePathComponent)(key);
+                key = helpers_js_1.unescapePathComponent(key);
             }
             if (banPrototypeModifications &&
                 (key == '__proto__' ||
@@ -213,10 +212,10 @@ function applyOperation(document, operation, validateOperation, mutateDocument,
                     key = obj.length;
                 }
                 else {
-                    if (validateOperation && !(0, helpers_js_1.isInteger)(key)) {
+                    if (validateOperation && !helpers_js_1.isInteger(key)) {
                         throw new exports.JsonPatchError("Expected an unsigned base-10 integer value, making the new referenced value the array element with the zero-based index", "OPERATION_PATH_ILLEGAL_ARRAY_INDEX", index, operation, document);
                     } // only parse key when it's an integer for `arr.prop` to work
-                    else if ((0, helpers_js_1.isInteger)(key)) {
+                    else if (helpers_js_1.isInteger(key)) {
                         key = ~~key;
                     }
                 }
@@ -273,7 +272,7 @@ function applyPatch(document, patch, validateOperation, mutateDocument, banProto
         }
     }
     if (!mutateDocument) {
-        document = (0, helpers_js_1._deepClone)(document);
+        document = helpers_js_1._deepClone(document);
     }
     var results = new Array(patch.length);
     for (var i = 0, length_1 = patch.length; i < length_1; i++) {
@@ -329,7 +328,7 @@ function validator(operation, index, document, existingPathFragment) {
     else if ((operation.op === 'add' || operation.op === 'replace' || operation.op === 'test') && operation.value === undefined) {
         throw new exports.JsonPatchError('Operation `value` property is not present (applicable in `add`, `replace` and `test` operations)', 'OPERATION_VALUE_REQUIRED', index, operation, document);
     }
-    else if ((operation.op === 'add' || operation.op === 'replace' || operation.op === 'test') && (0, helpers_js_1.hasUndefined)(operation.value)) {
+    else if ((operation.op === 'add' || operation.op === 'replace' || operation.op === 'test') && helpers_js_1.hasUndefined(operation.value)) {
         throw new exports.JsonPatchError('Operation `value` property is not present (applicable in `add`, `replace` and `test` operations)', 'OPERATION_VALUE_CANNOT_CONTAIN_UNDEFINED', index, operation, document);
     }
     else if (document) {
@@ -369,7 +368,7 @@ function validate(sequence, document, externalValidator) {
         }
         if (document) {
             //clone document and sequence so that we can safely try applying operations
-            applyPatch((0, helpers_js_1._deepClone)(document), (0, helpers_js_1._deepClone)(sequence), externalValidator || true);
+            applyPatch(helpers_js_1._deepClone(document), helpers_js_1._deepClone(sequence), externalValidator || true);
         }
         else {
             externalValidator = externalValidator || validator;
diff --git a/commonjs/duplex.js b/commonjs/duplex.js
index d2d0ebf..88975c6 100644
--- a/commonjs/duplex.js
+++ b/commonjs/duplex.js
@@ -1,5 +1,4 @@
 Object.defineProperty(exports, "__esModule", { value: true });
-exports.compare = exports.generate = exports.observe = exports.unobserve = void 0;
 /*!
  * https://github.com/Starcounter-Jack/JSON-Patch
  * (c) 2017-2021 Joachim Wester
@@ -57,7 +56,7 @@ function observe(obj, callback) {
         return observer;
     }
     observer = {};
-    mirror.value = (0, helpers_js_1._deepClone)(obj);
+    mirror.value = helpers_js_1._deepClone(obj);
     if (callback) {
         observer.callback = callback;
         observer.next = null;
@@ -102,7 +101,7 @@ function generate(observer, invertible) {
     var mirror = beforeDict.get(observer.object);
     _generate(mirror.value, observer.object, observer.patches, "", invertible);
     if (observer.patches.length) {
-        (0, core_js_1.applyPatch)(mirror.value, observer.patches);
+        core_js_1.applyPatch(mirror.value, observer.patches);
     }
     var temp = observer.patches;
     if (temp.length > 0) {
@@ -122,34 +121,34 @@ function _generate(mirror, obj, patches, path, invertible) {
     if (typeof obj.toJSON === "function") {
         obj = obj.toJSON();
     }
-    var newKeys = (0, helpers_js_1._objectKeys)(obj);
-    var oldKeys = (0, helpers_js_1._objectKeys)(mirror);
+    var newKeys = helpers_js_1._objectKeys(obj);
+    var oldKeys = helpers_js_1._objectKeys(mirror);
     var changed = false;
     var deleted = false;
     //if ever "move" operation is implemented here, make sure this test runs OK: "should not generate the same patch twice (move)"
     for (var t = oldKeys.length - 1; t >= 0; t--) {
         var key = oldKeys[t];
         var oldVal = mirror[key];
-        if ((0, helpers_js_1.hasOwnProperty)(obj, key) && !(obj[key] === undefined && oldVal !== undefined && Array.isArray(obj) === false)) {
+        if (helpers_js_1.hasOwnProperty(obj, key) && !(obj[key] === undefined && oldVal !== undefined && Array.isArray(obj) === false)) {
             var newVal = obj[key];
             if (typeof oldVal == "object" && oldVal != null && typeof newVal == "object" && newVal != null && Array.isArray(oldVal) === Array.isArray(newVal)) {
-                _generate(oldVal, newVal, patches, path + "/" + (0, helpers_js_1.escapePathComponent)(key), invertible);
+                _generate(oldVal, newVal, patches, path + "/" + helpers_js_1.escapePathComponent(key), invertible);
             }
             else {
                 if (oldVal !== newVal) {
                     changed = true;
                     if (invertible) {
-                        patches.push({ op: "test", path: path + "/" + (0, helpers_js_1.escapePathComponent)(key), value: (0, helpers_js_1._deepClone)(oldVal) });
+                        patches.push({ op: "test", path: path + "/" + helpers_js_1.escapePathComponent(key), value: helpers_js_1._deepClone(oldVal) });
                     }
-                    patches.push({ op: "replace", path: path + "/" + (0, helpers_js_1.escapePathComponent)(key), value: (0, helpers_js_1._deepClone)(newVal) });
+                    patches.push({ op: "replace", path: path + "/" + helpers_js_1.escapePathComponent(key), value: helpers_js_1._deepClone(newVal) });
                 }
             }
         }
         else if (Array.isArray(mirror) === Array.isArray(obj)) {
             if (invertible) {
-                patches.push({ op: "test", path: path + "/" + (0, helpers_js_1.escapePathComponent)(key), value: (0, helpers_js_1._deepClone)(oldVal) });
+                patches.push({ op: "test", path: path + "/" + helpers_js_1.escapePathComponent(key), value: helpers_js_1._deepClone(oldVal) });
             }
-            patches.push({ op: "remove", path: path + "/" + (0, helpers_js_1.escapePathComponent)(key) });
+            patches.push({ op: "remove", path: path + "/" + helpers_js_1.escapePathComponent(key) });
             deleted = true; // property has been deleted
         }
         else {
@@ -165,8 +164,8 @@ function _generate(mirror, obj, patches, path, invertible) {
     }
     for (var t = 0; t < newKeys.length; t++) {
         var key = newKeys[t];
-        if (!(0, helpers_js_1.hasOwnProperty)(mirror, key) && obj[key] !== undefined) {
-            patches.push({ op: "add", path: path + "/" + (0, helpers_js_1.escapePathComponent)(key), value: (0, helpers_js_1._deepClone)(obj[key]) });
+        if (!helpers_js_1.hasOwnProperty(mirror, key) && obj[key] !== undefined) {
+            patches.push({ op: "add", path: path + "/" + helpers_js_1.escapePathComponent(key), value: helpers_js_1._deepClone(obj[key]) });
         }
     }
 }
diff --git a/commonjs/helpers.js b/commonjs/helpers.js
index db0c6f5..5f2350e 100644
--- a/commonjs/helpers.js
+++ b/commonjs/helpers.js
@@ -7,19 +7,16 @@ var __extends = (this && this.__extends) || (function () {
     var extendStatics = function (d, b) {
         extendStatics = Object.setPrototypeOf ||
             ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
-            function (d, b) { for (var p in b) if (Object.prototype.hasOwnProperty.call(b, p)) d[p] = b[p]; };
+            function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
         return extendStatics(d, b);
     };
     return function (d, b) {
-        if (typeof b !== "function" && b !== null)
-            throw new TypeError("Class extends value " + String(b) + " is not a constructor or null");
         extendStatics(d, b);
         function __() { this.constructor = d; }
         d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
     };
 })();
 Object.defineProperty(exports, "__esModule", { value: true });
-exports.PatchError = exports.hasUndefined = exports.getPath = exports._getPathRecursive = exports.unescapePathComponent = exports.escapePathComponent = exports.isInteger = exports._deepClone = exports._objectKeys = exports.hasOwnProperty = void 0;
 var _hasOwnProperty = Object.prototype.hasOwnProperty;
 function hasOwnProperty(obj, key) {
     return _hasOwnProperty.call(obj, key);
@@ -125,7 +122,7 @@ function getPath(root, obj) {
     if (path === '') {
         throw new Error("Object not found in root");
     }
-    return "/".concat(path);
+    return "/" + path;
 }
 exports.getPath = getPath;
 /**
@@ -161,7 +158,7 @@ function patchErrorMessageFormatter(message, args) {
     for (var key in args) {
         var value = typeof args[key] === 'object' ? JSON.stringify(args[key], null, 2) : args[key]; // pretty print
         if (typeof value !== 'undefined') {
-            messageParts.push("".concat(key, ": ").concat(value));
+            messageParts.push(key + ": " + value);
         }
     }
     return messageParts.join('\n');
diff --git a/dist/fast-json-patch.js b/dist/fast-json-patch.js
index 0825c48..c0f4b80 100644
--- a/dist/fast-json-patch.js
+++ b/dist/fast-json-patch.js
@@ -1,4 +1,4 @@
-/*! fast-json-patch, version: 3.1.0 */
+/*! fast-json-patch, version: 3.1.1 */
 var jsonpatch =
 /******/ (function(modules) { // webpackBootstrap
 /******/ 	// The module cache
diff --git a/dist/fast-json-patch.min.js b/dist/fast-json-patch.min.js
index 9ab5c76..74a6a36 100644
--- a/dist/fast-json-patch.min.js
+++ b/dist/fast-json-patch.min.js
@@ -1,4 +1,4 @@
-/*! fast-json-patch, version: 3.1.0 */
+/*! fast-json-patch, version: 3.1.1 */
 var jsonpatch=function(e){var t={};function r(n){if(t[n])return t[n].exports;var o=t[n]={i:n,l:!1,exports:{}};return e[n].call(o.exports,o,o.exports,r),o.l=!0,o.exports}return r.m=e,r.c=t,r.d=function(e,t,n){r.o(e,t)||Object.defineProperty(e,t,{enumerable:!0,get:n})},r.r=function(e){"undefined"!=typeof Symbol&&Symbol.toStringTag&&Object.defineProperty(e,Symbol.toStringTag,{value:"Module"}),Object.defineProperty(e,"__esModule",{value:!0})},r.t=function(e,t){if(1&t&&(e=r(e)),8&t)return e;if(4&t&&"object"==typeof e&&e&&e.__esModule)return e;var n=Object.create(null);if(r.r(n),Object.defineProperty(n,"default",{enumerable:!0,value:e}),2&t&&"string"!=typeof e)for(var o in e)r.d(n,o,function(t){return e[t]}.bind(null,o));return n},r.n=function(e){var t=e&&e.__esModule?function(){return e.default}:function(){return e};return r.d(t,"a",t),t},r.o=function(e,t){return Object.prototype.hasOwnProperty.call(e,t)},r.p="",r(r.s=2)}([function(e,t){
 /*!
  * https://github.com/Starcounter-Jack/JSON-Patch
diff --git a/module/helpers.mjs b/module/helpers.mjs
index a090f68..592f560 100644
--- a/module/helpers.mjs
+++ b/module/helpers.mjs
@@ -7,12 +7,10 @@ var __extends = (this && this.__extends) || (function () {
     var extendStatics = function (d, b) {
         extendStatics = Object.setPrototypeOf ||
             ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
-            function (d, b) { for (var p in b) if (Object.prototype.hasOwnProperty.call(b, p)) d[p] = b[p]; };
+            function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
         return extendStatics(d, b);
     };
     return function (d, b) {
-        if (typeof b !== "function" && b !== null)
-            throw new TypeError("Class extends value " + String(b) + " is not a constructor or null");
         extendStatics(d, b);
         function __() { this.constructor = d; }
         d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
@@ -116,7 +114,7 @@ export function getPath(root, obj) {
     if (path === '') {
         throw new Error("Object not found in root");
     }
-    return "/".concat(path);
+    return "/" + path;
 }
 /**
 * Recursively checks whether an object has any undefined values inside.
@@ -150,7 +148,7 @@ function patchErrorMessageFormatter(message, args) {
     for (var key in args) {
         var value = typeof args[key] === 'object' ? JSON.stringify(args[key], null, 2) : args[key]; // pretty print
         if (typeof value !== 'undefined') {
-            messageParts.push("".concat(key, ": ").concat(value));
+            messageParts.push(key + ": " + value);
         }
     }
     return messageParts.join('\n');
diff --git a/package-lock.json b/package-lock.json
index 179ef01..cd21723 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "fast-json-patch",
-  "version": "3.2.0",
+  "version": "3.1.1",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "fast-json-patch",
-      "version": "3.2.0",
+      "version": "3.1.1",
       "license": "MIT",
       "devDependencies": {
         "benchmark": "^2.1.4",
diff --git a/package.json b/package.json
index 138c88b..688a6d0 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "fast-json-patch",
-    "version": "3.1.0",
+    "version": "3.1.1",
     "description": "Fast implementation of JSON-Patch (RFC-6902) with duplex (observe changes) capabilities",
     "homepage": "https://github.com/Starcounter-Jack/JSON-Patch",
     "keywords": [
@@ -62,4 +62,4 @@
         "bench-core": "node test/spec/coreBenchmark.js",
         "bench-duplex": "node test/spec/coreBenchmark.js && node test/spec/duplexBenchmark.js"
     }
-}
\ No newline at end of file
+}