alternatif olarak angularjs ile ;
<script type="text/javascript" src="angularjs.js"></script>
<script type="text/javascript">
function MenuController($scope) {
       $scope.bMenuA = false;
       $scope.bMenuB = false;
}
</script>
<body ng-app="">
<div class="header" ng-controller="MenuController">
      <div class="A" ng-click="bMenuA = !bMenuA; bMenuB = false"></div>
      <div class="B" ng-click="bMenuB = !bMenuB; bMenuA = false"></div>
</div>