diff --git a/.jshintrc b/.jshintrc
index 72c2b12..c4b19e9 100644
--- a/.jshintrc
+++ b/.jshintrc
@@ -1,4 +1,5 @@
 {
+  "esversion": 6,
   "bitwise": false, // Prohibits the use of bitwise operators (not confuse & with &&)
   "curly": true, // Requires to always put curly braces around blocks in loops and conditionals
   "eqeqeq": false, // Prohibits the use of == and != in favor of === and !==
@@ -28,6 +29,8 @@
     "Uint8ClampedArray": true,
     "ArrayBuffer": true,
     "Float32Array": true,
-    "Float64Array": true
+    "Float64Array": true,
+    "self": false,
+    "globalThis": false
   }
 }
diff --git a/src/cipher-core.js b/src/cipher-core.js
index 125632c..32e2205 100644
--- a/src/cipher-core.js
+++ b/src/cipher-core.js
@@ -772,15 +772,16 @@ CryptoJS.lib.Cipher || (function (undefined) {
             }
 
             // Derive key and IV
+            let key;
             if (!hasher) {
-                var key = EvpKDF.create({ keySize: keySize + ivSize }).compute(password, salt);
+                key = EvpKDF.create({ keySize: keySize + ivSize }).compute(password, salt);
             } else {
-                var key = EvpKDF.create({ keySize: keySize + ivSize, hasher: hasher }).compute(password, salt);
+                key = EvpKDF.create({ keySize: keySize + ivSize, hasher: hasher }).compute(password, salt);
             }
             
 
             // Separate key and IV
-            var iv = WordArray.create(key.words.slice(keySize), ivSize * 4);
+            const iv = WordArray.create(key.words.slice(keySize), ivSize * 4);
             key.sigBytes = keySize * 4;
 
             // Return params