Get last element in an object using angularjs

How to get the last element in an object?
Example:

$scope.sample =[
{“num” : “1”,
{“num”: “2”,
{“num”: “3”}
]
How can I get 3 and add it to 2? In short, how can I get the sum of the last 2 elements in an object?

Why not get the length of the $scope.sample by

$scope.sample.forEach(function(value,key){

 // Add element  3 to element 2
  var sum = 0;
   if(key > 0){
       
      sum = value.num + sum
   }
  console.log(sum) 

})

But I think $scope.sample[index] should work since first element start from index 0

2nd and 3rd element should be $scope.sample[1].num + $scope.sample[2].num

thanks but what if the user adds new element:

New input: 0
$scope.sample =[
{“num” : “1”},
{“num”: “2”},
{“num”: “3”},
{“num”: “0”}
]

Answer: 3 (0+3)

Then remove the if key
var sum = 0;
$scope.sample.forEach(function(value,key){

  sum = value.num + sum

console.log(sum)

})