I know that this question has an accepted answer but I thought I'd chip in with an alternative which uses array.reduce, seeing that summing an array is the canonical example for reduce:

Copy$scope.sum = function(items, prop){
    return items.reduce( function(a, b){
        return a + b[prop];
    }, 0);
};

$scope.travelerTotal = $scope.sum($scope.traveler, 'Amount');

Fiddle

It can be as simple as that:

const sumValues = obj => Object.values(obj).reduce((a, b) => a + b, 0);

Quoting MDN:

The Object.values() method returns an array of a given object's own enumerable property values, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well).

from Object.values() on MDN

The reduce() method applies a function against an accumulator and each value of the array (from left-to-right) to reduce it to a single value.

from Array.prototype.reduce() on MDN

You can use this function like that:

sumValues({a: 4, b: 6, c: -5, d: 0}); // gives 5

Note that this code uses some ECMAScript features which are not supported by some older browsers (like IE). You might need to use Babel to compile your code.

Use Array.prototype.reduce(), the reduce() method applies a function against an accumulator and each value of the array (from left-to-right) to reduce it to a single value.

var array = [{
  "adults": 2,
  "children": 3
}, {
  "adults": 2,
  "children": 1
}];

var val = array.reduce(function(previousValue, currentValue) {
  return {
    adults: previousValue.adults + currentValue.adults,
    children: previousValue.children + currentValue.children
  }
});
console.log(val);

try with simply use Object.keys() and Array#map() function

obj1 = {
  'over_due_data': 10,
  'text_data': 5
}
obj2 = {
  'over_due_data': 20,
  'text_data': 5
}
var obj ={}
Object.keys(obj1).forEach(function(a){
  obj[a] = obj1[a] +obj2[a]

})
console.log(obj)