Javascript Data Type How to - Sum objects' property within an array

Question

We would like to know how to sum objects' property within an array.

Answer


<!DOCTYPE html>
<html>
<head>
<script type='text/javascript'>
<!-- www. j a v  a2 s .  c  om-->
var arr = [{"year": 2011, "num": 0}, {"year": 2012, "num": 2}, {"year": 2013, "num": 5}];
var sum = 0;
for(var obj in arr) {
    sum += arr[obj].num;
}

document.writeln(sum);

</script>
</head>
<body>
</body>
</html>

The code above is rendered as follows: