diff --git a/src/js/core/state_manager.js b/src/js/core/state_manager.js
index 6045675f..733fce5e 100644
--- a/src/js/core/state_manager.js
+++ b/src/js/core/state_manager.js
@@ -69,7 +69,7 @@ export class StateManager {
 
             // Remove all references
             for (const stateKey in this.currentState) {
-                if (this.currentState.hasOwnProperty(stateKey)) {
+                if (Object.hasOwn(this.currentState, stateKey)) {
                     delete this.currentState[stateKey];
                 }
             }
diff --git a/src/js/game/hud/parts/building_placer_logic.js b/src/js/game/hud/parts/building_placer_logic.js
index c25f4210..37cf8710 100644
--- a/src/js/game/hud/parts/building_placer_logic.js
+++ b/src/js/game/hud/parts/building_placer_logic.js
@@ -159,7 +159,7 @@ export class HUDBuildingPlacerLogic extends BaseHUDPart {
             return this.currentBaseRotationGeneral;
         }
         const metaBuilding = this.currentMetaBuilding.get();
-        if (metaBuilding && this.preferredBaseRotations.hasOwnProperty(metaBuilding.getId())) {
+        if (metaBuilding && Object.hasOwn(this.preferredBaseRotations, metaBuilding.getId())) {
             return this.preferredBaseRotations[metaBuilding.getId()];
         } else {
             return this.currentBaseRotationGeneral;
diff --git a/src/js/game/root.js b/src/js/game/root.js
index 6f751e73..b41d76c4 100644
--- a/src/js/game/root.js
+++ b/src/js/game/root.js
@@ -224,8 +224,8 @@ export class GameRoot {
         }
 
         // Finally free all properties
-        for (let prop in this) {
-            if (this.hasOwnProperty(prop)) {
+        for (const prop in this) {
+            if (Object.hasOwn(this, prop)) {
                 delete this[prop];
             }
         }
diff --git a/src/js/profile/application_settings.js b/src/js/profile/application_settings.js
index 22133d00..6f98a14c 100644
--- a/src/js/profile/application_settings.js
+++ b/src/js/profile/application_settings.js
@@ -375,7 +375,7 @@ export class ApplicationSettings extends ReadWriteProxy {
      * @param {string} key
      */
     getSetting(key) {
-        assert(this.getAllSettings().hasOwnProperty(key), "Setting not known: " + key);
+        assert(Object.hasOwn(this.getAllSettings(), key), "Setting not known: " + key);
         return this.getAllSettings()[key];
     }
 
diff --git a/src/js/savegame/serialization.js b/src/js/savegame/serialization.js
index 542dbdf3..2e587f85 100644
--- a/src/js/savegame/serialization.js
+++ b/src/js/savegame/serialization.js
@@ -18,11 +18,11 @@ import {
     TypeNumber,
     TypePair,
     TypePositiveInteger,
+    TypePositiveIntegerOrString,
     TypePositiveNumber,
     TypeString,
     TypeStructuredObject,
     TypeVector,
-    TypePositiveIntegerOrString,
 } from "./serialization_data_types";
 
 /**
@@ -239,12 +239,9 @@ export class BasicSerializableObject {
  */
 export function serializeSchema(obj, schema, mergeWith = {}) {
     for (const key in schema) {
-        if (!obj.hasOwnProperty(key)) {
+        if (!Object.hasOwn(obj, key)) {
             logger.error("Invalid schema, property", key, "does not exist on", obj, "(schema=", schema, ")");
-            assert(
-                obj.hasOwnProperty(key),
-                "serialization: invalid schema, property does not exist on object: " + key
-            );
+            assert(false, "serialization: invalid schema, property does not exist on object: " + key);
         }
         if (!schema[key]) {
             assert(false, "Invalid schema (bad key '" + key + "'): " + JSON.stringify(schema));
@@ -292,7 +289,7 @@ export function deserializeSchema(obj, schema, data, baseclassErrorResult = null
     }
 
     for (const key in schema) {
-        if (!data.hasOwnProperty(key)) {
+        if (!Object.hasOwn(data, key)) {
             logger.error("Data", data, "does not contain", key, "(schema:", schema, ")");
             return "Missing key in schema: " + key + " of class " + obj.constructor.name;
         }
@@ -325,7 +322,7 @@ export function deserializeSchema(obj, schema, data, baseclassErrorResult = null
  */
 export function verifySchema(schema, data) {
     for (const key in schema) {
-        if (!data.hasOwnProperty(key)) {
+        if (!Object.hasOwn(data, key)) {
             logger.error("Data", data, "does not contain", key, "(schema:", schema, ")");
             return "verify: missing key required by schema in stored data: " + key;
         }
@@ -352,7 +349,7 @@ export function extendSchema(base, newOne) {
     /** @type {Schema} */
     const result = Object.assign({}, base);
     for (const key in newOne) {
-        if (result.hasOwnProperty(key)) {
+        if (Object.hasOwn(result, key)) {
             logger.error("Extend schema got duplicate key:", key);
             continue;
         }