JavaScript sum array of objects | Example code

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Use Array reduce() method to sum an array of objects in JavaScript. This method applies a function against an accumulator and each value of the array (from left to right) to reduce it to a single value.

JavaScript sum array of objects

Simple example code.

<!DOCTYPE html>
<html>
<body>

  <script>
   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);
</script>

</body>
</html> 

Output:

JavaScript sum array of objects

One line solution for the same but adding all values of object property

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

    var totalChild = array.reduce((accum,item) => accum + item.children, 0)

    console.log(totalChild)
</script>

Output: 4

You can write a function for this task, which gets the array to iterate over a property, which value should be added.

The key feature of the function is the Array#reduce method and a property which returns the actual count value and the actual property value.

function count(array, key) {
    return array.reduce(function (r, a) {
        return r + a[key];
    }, 0);
}

var array = [{ "adults": 2, "children": 3 }, { "adults": 2, "children": 2 }],
    adults = count(array, 'adults'),
    children = count(array, 'children');

document.write('Adults: ' + adults + '<br>');
document.write('Children: ' + children + '<br>');

Output:

Adults: 4
Children: 5

Do comment if you have any doubts or suggestions on this JS Array topic.

Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.

OS: Windows 10

Code: HTML 5 Version

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