diff --git a/.eslintrc b/.eslintrc
index 74a50f7c0b2e740e42c9b526f923364f5ad6f1a0..9f8d2af310fbd63e70301187cba4b8b468bb3c34 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -10,6 +10,7 @@
   ],
   "globals": {
     "Address": true,
+    "Environment": true,
     "fileGuard": true,
     "files": true,
     "Header": true,
diff --git a/core/constants.js b/core/constants.js
index fd4691e5882ef7cd5adbdd715774e40d78ce8970..6ed9dfce01fbc20038858a7368a57a4942e4e384 100644
--- a/core/constants.js
+++ b/core/constants.js
@@ -32,6 +32,11 @@ const Address = {
     'WWW_PREFIX': 'www.'
 };
 
+const Environment = {
+    'STABLE': 'stable',
+    'STAGING': 'staging'
+};
+
 const Header = {
     'COOKIE': 'Cookie',
     'ORIGIN': 'Origin',
diff --git a/core/files.js b/core/files.js
index da25e3e239df5ab8b2abd4818f8a1846102c610a..80ca8b40c3d751d1ce91d81af90d6aecc5e63b00 100644
--- a/core/files.js
+++ b/core/files.js
@@ -20,7 +20,7 @@
 var files = {
 
     // Files [Stable]
-    'stable': {
+    [Environment.STABLE]: {
 
         // AngularJS
         'resources/angularjs/1.0.1/angular.min.jsm': true,
@@ -265,7 +265,7 @@ var files = {
     },
 
     // Files [Staging]
-    'staging': {
+    [Environment.STAGING]: {
 
         // AngularJS
         'resources/angularjs/1.5.8/angular.min.jsm': true,
diff --git a/core/main.js b/core/main.js
index 58283af860d4f79c446bc1a383a28936378457cb..73e2769091aac6afb52e4c5e317cadbc796bc1a6 100644
--- a/core/main.js
+++ b/core/main.js
@@ -42,9 +42,9 @@ main._initializeSettings = function () {
         }
 
         if (items.blockMissing === true || items.enforceStaging === true) {
-            stateManager.updateEnvironment('staging');
+            stateManager.updateEnvironment(Environment.STAGING);
         } else {
-            stateManager.updateEnvironment('stable');
+            stateManager.updateEnvironment(Environment.STABLE);
         }
 
         if (items.disablePrefetch !== false) {
diff --git a/core/request-sanitizer.js b/core/request-sanitizer.js
index 8a76e6759e69b916707d0d0ee8260d38a241f5ff..8951ec1c46775d5f3698489df822b4889e0b8e84 100644
--- a/core/request-sanitizer.js
+++ b/core/request-sanitizer.js
@@ -65,9 +65,9 @@ requestSanitizer._stripMetadata = function (requestDetails) {
  * Initializations
  */
 
-chrome.storage.local.get({[Setting.STRIP_METADATA]: true}, function (options) {
+chrome.storage.local.get({[Setting.STRIP_METADATA]: true}, function (items) {
 
-    if (options === null || options.stripMetadata !== false) {
+    if (items === null || items.stripMetadata !== false) {
         requestSanitizer.enable();
     }
 });
diff --git a/core/state-manager.js b/core/state-manager.js
index f5e1147748636bc85d427400e3fc36e011e02506..a21bba118979665dc9eb2d316a314c87414e9916 100644
--- a/core/state-manager.js
+++ b/core/state-manager.js
@@ -70,12 +70,12 @@ stateManager.registerInjection = function (tabIdentifier, injection) {
 
 stateManager.setEnvironment = function (environment) {
 
-    if (environment === 'stable') {
+    if (environment === Environment.STABLE) {
 
         // Strike a balance between coverage and website stability.
         files.active = files.stable;
 
-    } else if (environment === 'staging') {
+    } else if (environment === Environment.STAGING) {
 
         // Improve coverage at the expense of website stability.
         files.active = Object.assign({}, files.stable, files.staging);
@@ -86,24 +86,24 @@ stateManager.updateEnvironment = function (preferredEnvironment) {
 
     return new Promise((resolve) => {
 
-        if (preferredEnvironment === 'stable') {
+        if (preferredEnvironment === Environment.STABLE) {
 
             let requiredItems = [Setting.BLOCK_MISSING, Setting.ENFORCE_STAGING];
 
             chrome.storage.local.get(requiredItems, function (items) {
 
                 if (items.blockMissing === true || items.enforceStaging === true) {
-                    stateManager.setEnvironment('staging');
+                    stateManager.setEnvironment(Environment.STAGING);
                 } else {
-                    stateManager.setEnvironment('stable');
+                    stateManager.setEnvironment(Environment.STABLE);
                 }
 
                 resolve();
             });
 
-        } else if (preferredEnvironment === 'staging') {
+        } else if (preferredEnvironment === Environment.STAGING) {
 
-            stateManager.setEnvironment('staging');
+            stateManager.setEnvironment(Environment.STAGING);
             resolve();
         }
     });
@@ -205,18 +205,18 @@ stateManager._handleStorageChanged = function (changes) {
     if (Setting.BLOCK_MISSING in changes) {
 
         if (changes.blockMissing.newValue === true) {
-            stateManager.updateEnvironment('staging');
+            stateManager.updateEnvironment(Environment.STAGING);
         } else {
-            stateManager.updateEnvironment('stable');
+            stateManager.updateEnvironment(Environment.STABLE);
         }
     }
 
     if (Setting.ENFORCE_STAGING in changes) {
 
         if (changes.enforceStaging.newValue === true) {
-            stateManager.updateEnvironment('staging');
+            stateManager.updateEnvironment(Environment.STAGING);
         } else {
-            stateManager.updateEnvironment('stable');
+            stateManager.updateEnvironment(Environment.STABLE);
         }
     }