diff --git a/src/vierbergenlars/LibJs/JSArray.php b/src/vierbergenlars/LibJs/JSArray.php
index 43d48c7..0b56b53 100644
--- a/src/vierbergenlars/LibJs/JSArray.php
+++ b/src/vierbergenlars/LibJs/JSArray.php
@@ -150,49 +150,49 @@ public function __get($name)
     }
 
 
-    public function current()
+    public function current(): mixed
     {
         return $this->_convert(current($this->array));
     }
 
-    public function key()
+    public function key(): mixed
     {
         return $this->_convert(key($this->array));
     }
 
-    public function next()
+    public function next(): void
     {
-        return $this->_convert(next($this->array));
+        $this->_convert(next($this->array));
     }
 
-    public function offsetExists($offset)
+    public function offsetExists(mixed $offset): bool
     {
         return isset($this->array[$offset]);
     }
 
-    public function offsetGet($offset)
+    public function offsetGet(mixed $offset): mixed
     {
         if(!$this->offsetExists($offset))
             return null;
         return $this->_convert($this->array[$offset]);
     }
 
-    public function offsetSet($offset, $value)
+    public function offsetSet(mixed $offset, mixed $value): void
     {
         $this->array[$offset] = $value;
     }
 
-    public function offsetUnset($offset)
+    public function offsetUnset(mixed $offset): void
     {
         unset($this->array[$offset]);
     }
 
-    public function rewind()
+    public function rewind(): void
     {
-        return reset($this->array);
+        reset($this->array);
     }
 
-    public function valid()
+    public function valid(): bool
     {
         return key($this->array) !== null;
     }
diff --git a/src/vierbergenlars/LibJs/JString.php b/src/vierbergenlars/LibJs/JString.php
index a006ac6..ff4448f 100644
--- a/src/vierbergenlars/LibJs/JString.php
+++ b/src/vierbergenlars/LibJs/JString.php
@@ -207,22 +207,22 @@ public function __get($name)
         }
     }
 
-    public function offsetExists($offset)
+    public function offsetExists(mixed $offset): bool
     {
         return isset($this->str[$offset]);
     }
 
-    public function offsetGet($offset)
+    public function offsetGet(mixed $offset): mixed
     {
         return $this->str[$offset];
     }
 
-    public function offsetSet($offset, $value)
+    public function offsetSet(mixed $offset, mixed $value): void
     {
         $this->str[$offset] = $value;
     }
 
-    public function offsetUnset($offset)
+    public function offsetUnset(mixed $offset): void
     {
         throw new \LogicException('Cannot unset a position in a string');
     }