Creating common controller functions

The way to define common code in angular is through Services.

You would define a new service like so :

.factory('CommonCode', function ($window) {
        var root = {};
        root.show = function(msg){
            $window.alert(msg);
        };
        return root;
    });

In your controller you would inject this service..like so

function MainAppCtrl($scope,CommonCode)
{
     $scope.alerter = CommonCode;
     $scope.alerter.show("Hello World");
}

Just include CommonCode as an argument to your controller function.. Angular will take care of injecting it for you ( Read on Dependancy Injection ..to understand what is happening here. )