AngularJS Example:

HTML

<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap.css">
<div ng-app>
    <div ng-controller="A"><input ng-model="m">
        {{a()}} - {{counter}}
    </div>
    <div ng-controller="B"><input ng-model="m">
        {{b()}} - {{counter}}
    </div>
</div>

JavaScript

function A($scope) {
    $scope.m='a';
    $scope.counter = 0;
    $scope.a = function(){
        $scope.counter++;
        return $scope.m;
    }
}
function B($scope) {
    $scope.m='b';
    $scope.counter = 0;
    $scope.b = function(){
        $scope.counter++;
        return $scope.m;
    }
}