Samples: grid-external-filtering

I want to do something like this:

//controller.public.js
import BaseController from './controller.js'

var lastValue;

class GridExternalFilteringGridExternalFilteringCtrl extends BaseController {
  constructor($scope, $injector, stateData) {
    super($scope, $injector);
  }

  // Fired when custom html section is loaded
  includeContentLoaded() {
  }

  // Fired when custom html section loading failed
  includeContentError(e) {

  }

  // Fired when view content is loaded
  onShow($scope) {
    console.log('Show');
  }

    changeHandler(e) {
       lastValue = e.value;
   this.examplefilter ( ).
   }

  exampleFilter ( ) {
    var filter;
    if ( lastValue gt "" ) {

      filter = {
                logic: 'or',
                filters: [
	 { field: 'Name', operator: 'contains', value: lastValue },
   	{ field: 'Address', operator: 'contains', value: lastValue }, 
 	{ field: 'Phone', operator: 'contains', value: lastValue },
 	{ field: 'SalesRep', operator: 'contains', value: lastValue },
	{ field: 'State', operator: 'contains', value: lastValue },
	{ field: 'Country', operator: 'contains', value: lastValue }
             ]
    };

    this.$ds.customerDs.filter(filter);

 } 

...

However, my component is a comboxbox and e.value is always undefined (via console.log)

Is there something intrinsically wrong with this approach? 

I'm assuming e is some sort of event object. 

In my real app I do not have a textbox, I have 3 comboboxes. 

How do I get the value of a combobox? 

Given e, is there a way I can tell which component generated the event?