SO Caculator Example

JavaScript

var $scope = {
    operator: null,
    answer: null,
    leftOperand: null,
    rightOperand: null,
};

$scope.setOperand = function (operand) {
    (function(prop){
        $scope[prop] = +$scope[prop] + operand
    })
    (['leftOperand','rightOperand'].reduce(function(t, k){
    console.log(t, $scope[t], k, $scope[k]);
        return !+$scope[k] ? k : t;
    }));
};

$scope.setOperand(6);
$scope.setOperand(6);
$scope.operator = '-';
$scope.setOperand(6);
$scope.setOperand(6);

console.log($scope);