Angular: Empty Fiddle

http://angularjs.org/

HTML

<script src="http://code.angularjs.org/angular-1.0.1.js"></script>
<div ng-controller="MyCtrl">
 Subtot:
  {{subtotal}}

</div>

JavaScript

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


myApp.controller('MyCtrl', function($scope){

  $scope.item = [
    {fieldName: "fname1", value: 2},
    {fieldName: "fname2", value: 5},
    {fieldName: "fname3", value: 4},
    {fieldName: "fname4", value: 6},
    {fieldName: "fname5", value: 3},
    {fieldName: "subTotal1", expression: "['fname1'] + ['fname2'] +['fname3'] +['fname4'] +['fname5'] +"}
  ]
  
  var subtotal=0;
  var subTotalPropertyValue = "subTotal1";
  var subTotalProperty = $scope.item.filter(function(o){
      if(o.fieldName == subTotalPropertyValue)
        return o;
  });
  
  if(subTotalProperty.length>0){
  	var expressionArray = subTotalProperty[0].expression.replace(/\s/g,"").split('+');
    
    var formattedArray={};   
    $scope.item.map(function(v,o){
       formattedArray[v.fieldName]=v.value;
       return v;
    });

    for(var i=0;i<expressionArray.length;i++){
       if(expressionArray[i]!=""){
       		var property= expressionArray[i].replace('[','').replace(']','').replace("'","").replace("'","");
					var value = formattedArray[property];
          subtotal += value;
       }
    }

$scope.subtotal=subtotal;
  }
  
})