# Reduce throws “NaN” in JavaScript?

I am trying to sum items in array. While searching Google and Stack Overflow I found that reduce is a good way of summing an array items. But, when there isn’t any key value pair reduce throws error as “Nah”, so how to deal with it?

My array exam:

```const array = [
{
key: '0',
value: '10',
pair: '2'
},
{
key: '0',
value: '10'
}
];
```

So from above, I need to calculate all the key values including pair. But when I use it on reduce it gives NaN as the second object doesn’t have ‘pair’,

How to deal this?

My code:

```array.reduce((a, b) => a + ((+b.key)+(+b.value)+(+b.pair)), 0)

```

So how to handle this “NaN”

You could use the new nullish coalescing operator, or since you know these are either numbers or non-existent and you want to us `0` in the non-existent case, the logical `||` operator:

```const array = [
{
key: '0',
value: '10',
pair: '2'
},
{
key: '0',
value: '10'
}
];

const result = array.reduce((a, b) => a + ((+b.key)+(+b.value)+(+(b.pair ?? 0))), 0);
// −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−^^^^^^^^^^^^^^
//                                                         Or   +(b.pair || 0)
console.log(result);```

You don’t need all of those `()`, though:

```const array = [
{
key: '0',
value: '10',
pair: '2'
},
{
key: '0',
value: '10'
}
];

const result = array.reduce((a, b) => a + ((+b.key)+(+b.value)+(+(b.pair ?? 0))), 0);
// −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−^^^^^^^^^^^^^^
//                                                         Or   +(b.pair || 0)
console.log(result);```