someClass = Ext.extend(someClassB, {
        _someFunctionC{  
           someButton = new Ext.button({  
              handler: function () {
                            this._onClick('click');
                       }
           }),
           _onClick(someMessage){
               Ext.Msg.alert(someMessage);
            }
        }
    }

_onClick eats one parameter; in the above code you put in the 'click' event because you want _onClick to be executed after the user clicks on the button. However, how do you specify this specific 'click' registration AND pass in a local variable as the _onClick parameter at the same time?

As an aside, why do you even have to specify 'click', when the API states that handler always pertains to a click? Is this additional information not unnecessary?