diff --git a/.eslintrc.json b/.eslintrc.json
index e7ca071..e1d4de0 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -29,6 +29,7 @@
 		"brace-style": ["error", "stroustrup", {"allowSingleLine": true}],
 		"comma-spacing": ["error", { "before": false, "after": true }],
 		"complexity": ["warn", 20],
+		"consistent-return": "error",
 		"constructor-super": "warn",
 		"eqeqeq": "error",
 		"eslint-comments/no-use": ["error", {"allow": ["eslint-disable-next-line"]}],
diff --git a/lib/iframeProtection.js b/lib/iframeProtection.js
index 95d0278..dc1f838 100644
--- a/lib/iframeProtection.js
+++ b/lib/iframeProtection.js
@@ -45,7 +45,7 @@
 		}
 		else {
 			if (isWhitelisted(window.location)){
-				return;
+				return false;
 			}
 		}
 		return changeProperty;
@@ -265,6 +265,10 @@
 	scope.protect = function protect(window, wrappedWindow, singleCallback, allCallback){
 		const changeProperty = createChangeProperty(window);
 		
+		if (!changeProperty){
+			return;
+		}
+		
 		const api = {window, wrappedWindow, changeProperty, singleCallback, allCallback};
 		
 		protectFrameProperties(api);
diff --git a/lib/intercept.js b/lib/intercept.js
index 56dee6f..58c7588 100644
--- a/lib/intercept.js
+++ b/lib/intercept.js
@@ -174,7 +174,7 @@
 									functionName: name,
 									dataURL: false
 								});
-								return;
+								return undef;
 							}
 						}, windowToProcess),
 						set: exportFunction(function(){}, windowToProcess)
diff --git a/lib/logging.js b/lib/logging.js
index ac98d44..50c1e9d 100644
--- a/lib/logging.js
+++ b/lib/logging.js
@@ -20,6 +20,7 @@
 		}
 		else {
 			warning("logging: Settings can only be set once.");
+			return settings.loaded;
 		}
 	};
 	
diff --git a/lib/modifiedScreenAPI.js b/lib/modifiedScreenAPI.js
index 9630ca2..02c2127 100644
--- a/lib/modifiedScreenAPI.js
+++ b/lib/modifiedScreenAPI.js
@@ -89,6 +89,26 @@
 		return window.screen;
 	}
 	
+	function fakeWidth(args, check){
+		const {prefs, notify, window, original} = check;
+		const originalValue = original.apply(this, window.Array.from(args));
+		const returnValue = Math.round(getScreenDimensions(prefs, window).width);
+		if (originalValue !== returnValue){
+			notify("fakedScreenReadout");
+		}
+		return returnValue;
+	}
+	
+	function fakeHeight(args, check){
+		const {prefs, notify, window, original} = check;
+		const originalValue = original.apply(this, window.Array.from(args));
+		const returnValue = Math.round(getScreenDimensions(prefs, window).height);
+		if (originalValue !== returnValue){
+			notify("fakedScreenReadout");
+		}
+		return returnValue;
+	}
+	
 	scope.changedGetters = [
 		{
 			objectGetters: [function(window){return window.Screen && window.Screen.prototype;}],
@@ -96,15 +116,7 @@
 			getterGenerator: function(checker){
 				const temp = {
 					get width(){
-						return checkerWrapper(checker, this, arguments, function(args, check){
-							const {prefs, notify, window, original} = check;
-							const originalValue = original.apply(this, window.Array.from(args));
-							const returnValue = Math.round(getScreenDimensions(prefs, window).width);
-							if (originalValue !== returnValue){
-								notify("fakedScreenReadout");
-							}
-							return returnValue;
-						});
+						return checkerWrapper(checker, this, arguments, fakeWidth);
 					}
 				};
 				return Object.getOwnPropertyDescriptor(temp, "width").get;
@@ -116,15 +128,7 @@
 			getterGenerator: function(checker){
 				const temp = {
 					get height(){
-						return checkerWrapper(checker, this, arguments, function(args, check){
-							const {prefs, notify, window, original} = check;
-							const originalValue = original.apply(this, window.Array.from(args));
-							const returnValue = Math.round(getScreenDimensions(prefs, window).height);
-							if (originalValue !== returnValue){
-								notify("fakedScreenReadout");
-							}
-							return returnValue;
-						});
+						return checkerWrapper(checker, this, arguments, fakeHeight);
 					}
 				};
 				return Object.getOwnPropertyDescriptor(temp, "height").get;
@@ -136,15 +140,7 @@
 			getterGenerator: function(checker){
 				const temp = {
 					get availWidth(){
-						return checkerWrapper(checker, this, arguments, function(args, check){
-							const {prefs, notify, window, original} = check;
-							const originalValue = original.apply(this, window.Array.from(args));
-							const returnValue = Math.round(getScreenDimensions(prefs, window).width);
-							if (originalValue !== returnValue){
-								notify("fakedScreenReadout");
-							}
-							return returnValue;
-						});
+						return checkerWrapper(checker, this, arguments, fakeWidth);
 					}
 				};
 				return Object.getOwnPropertyDescriptor(temp, "availWidth").get;
@@ -156,15 +152,7 @@
 			getterGenerator: function(checker){
 				const temp = {
 					get availHeight(){
-						return checkerWrapper(checker, this, arguments, function(args, check){
-							const {prefs, notify, window, original} = check;
-							const originalValue = original.apply(this, window.Array.from(args));
-							const returnValue = Math.round(getScreenDimensions(prefs, window).height);
-							if (originalValue !== returnValue){
-								notify("fakedScreenReadout");
-							}
-							return returnValue;
-						});
+						return checkerWrapper(checker, this, arguments, fakeHeight);
 					}
 				};
 				return Object.getOwnPropertyDescriptor(temp, "availHeight").get;
diff --git a/lib/settings.js b/lib/settings.js
index a639586..d2e4ded 100644
--- a/lib/settings.js
+++ b/lib/settings.js
@@ -146,6 +146,7 @@
 				}
 				else {
 					logging.warning("Transient setting %s cannot be stored.", name);
+					return Promise.reject("Transient setting " + name + " cannot be stored.");
 				}
 			};
 			
@@ -162,6 +163,7 @@
 					}
 					else{
 						logging.warning("Invalid value for %s (%s):", name, url, newValue);
+						return Promise.reject("Invalid value for " + name + " (" + url + "): " + newValue);
 					}
 				};
 			}
@@ -173,6 +175,7 @@
 					}
 					else{
 						logging.warning("Invalid value for %s:", name, newValue);
+						return Promise.reject("Invalid value for " + name + ": " + newValue);
 					}
 				};
 			}
@@ -307,6 +310,7 @@
 		}
 		else {
 			logging.error("Try to set unknown setting:", name);
+			return Promise.reject("Try to set unknown setting: " + name);
 		}
 	};
 	scope.get = function(name, ...args){
@@ -316,6 +320,7 @@
 		}
 		else {
 			logging.error("Try to get unknown setting:", name);
+			return undefined;
 		}
 	};
 
diff --git a/options/options.js b/options/options.js
index cd09237..ec64241 100644
--- a/options/options.js
+++ b/options/options.js
@@ -614,7 +614,7 @@
 					if (reallyShare){
 						return this.originalSet(value, ...args);
 					}
-					return;
+					return false;
 				}).catch(function(error){
 					logging.warning("Unable to set sharePersistentRndBetweenDomains:", error);
 				});
diff --git a/options/whitelist.js b/options/whitelist.js
index d238d8c..440d789 100644
--- a/options/whitelist.js
+++ b/options/whitelist.js
@@ -85,6 +85,7 @@
 						setSelect.selectedIndex = index;
 						return true;
 					}
+					return false;
 				}) &&
 				searchParameters.has("domain")
 			){
diff --git a/pageAction/pageAction.js b/pageAction/pageAction.js
index 37790e6..14f908c 100644
--- a/pageAction/pageAction.js
+++ b/pageAction/pageAction.js
@@ -65,7 +65,7 @@
 					if (choice){
 						return settings.set("showNotifications", false, choice);
 					}
-					return;
+					return false;
 				}).then(function(){
 					return window.close();
 				});
@@ -123,7 +123,7 @@
 					if (choice){
 						return settings.set(setting.name, setting.value, choice);
 					}
-					return;
+					return false;
 				}).then(function(){
 					return window.close();
 				});
@@ -142,7 +142,7 @@
 					if (choice){
 						return lists.appendTo("sessionWhite", choice);
 					}
-					return;
+					return false;
 				}).then(function(){
 					return window.close();
 				});
diff --git a/releaseNotes.txt b/releaseNotes.txt
index a75bc42..b6e34d6 100644
--- a/releaseNotes.txt
+++ b/releaseNotes.txt
@@ -1,6 +1,7 @@
 Version 0.5.15:
 	changes:
 		- improved storage of protected API features
+		- code cleanup
 	
 	new features:
 		- added screen protection