Angular: Empty Fiddle

http://angularjs.org/

HTML

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.14/angular.min.js"></script>
<div  ng-controller="MyCtrl">
    <input type="text" ng-model="potatoCount" ng-keyup="onKeyup($event, 'potatoCount')" />
</div>

JavaScript

var myApp = angular.module('myApp',[]);
    

function MyCtrl($scope) {
    $scope.onKeyup = function (evt, val) {
        if(evt.keyCode === 40) {
            --$scope[val];
            console.log("decrementing val");
        } else if (evt.keyCode === 38) {
            ++$scope[val];
            console.log("incrementing val");
        }
    };
    $scope.potatoCount = 42;
}