Cannot set property error in Angular js

the following is code shows cannot set property 'show' of undefined in angular js

HTML code

<div ng-controller="DeathRayMenuController">
<button ng-click="toggleMenu()">Toggle</button>
<ul ng-show="menuState.show">
<li ng-click="stun()">Stun</li>
<li ng-click="disintegrate()">Disintegrate</li>
<li ng-click="destroy()">Destroy</li>
</ul>

Javascript :

   function DeathRayMenuController($scope) {
     $scope.menuState.show = false;

     $scope.toggleMenu = function() {
         $scope.menuState.show = true;
     }
}

While running this im getting this error

TypeError: Cannot set property 'show' of undefined