3 files changed, 7 insertions, 3 deletions
diff --git a/ext/mixed/js/audio.js b/ext/mixed/js/audio.js
index 4e9d04fa..7d5ffedd 100644
--- a/ext/mixed/js/audio.js
+++ b/ext/mixed/js/audio.js
@@ -113,7 +113,7 @@ function audioGetFromUrl(url, willDownload) {
 
 async function audioGetFromSources(expression, sources, optionsContext, willDownload, cache=null) {
     const key = `${expression.expression}:${expression.reading}`;
-    if (cache !== null && cache.hasOwnProperty(expression)) {
+    if (cache !== null && hasOwn(cache, expression)) {
         return cache[key];
     }
 
diff --git a/ext/mixed/js/core.js b/ext/mixed/js/core.js
index 8a8a2368..d82b9b4b 100644
--- a/ext/mixed/js/core.js
+++ b/ext/mixed/js/core.js
@@ -94,6 +94,10 @@ function isObject(value) {
     return typeof value === 'object' && value !== null && !Array.isArray(value);
 }
 
+function hasOwn(object, property) {
+    return Object.prototype.hasOwnProperty.call(object, property);
+}
+
 // toIterable is required on Edge for cross-window origin objects.
 function toIterable(value) {
     if (typeof Symbol !== 'undefined' && typeof value[Symbol.iterator] !== 'undefined') {
diff --git a/ext/mixed/js/display.js b/ext/mixed/js/display.js
index 854418f4..ce43b22c 100644
--- a/ext/mixed/js/display.js
+++ b/ext/mixed/js/display.js
@@ -194,7 +194,7 @@ class Display {
     onKeyDown(e) {
         const key = Display.getKeyFromEvent(e);
         const handlers = Display.onKeyDownHandlers;
-        if (handlers.hasOwnProperty(key)) {
+        if (hasOwn(handlers, key)) {
             const handler = handlers[key];
             if (handler(this, e)) {
                 e.preventDefault();
@@ -216,7 +216,7 @@ class Display {
 
     onRuntimeMessage({action, params}, sender, callback) {
         const handlers = Display.runtimeMessageHandlers;
-        if (handlers.hasOwnProperty(action)) {
+        if (hasOwn(handlers, action)) {
             const handler = handlers[action];
             const result = handler(this, params);
             callback(result);