Reduce throws "NaN" in JavaScript?

user_14862914 0
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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"

arrays javascript
4 Answers

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);

user_1572470

Try this,

array.reduce((a, b) => a + ((+b.key||0)+(+b.value||0)+(+b.pair||0)), 0)
user_141443010

You need to get the sum of the values in each iteration, and check if the value is a Number:

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

const res = array.reduce((a, b) => 
  a + Object.values(b).reduce((acc, value) => acc + (isNaN(value)?0:+value), 0)
, 0);

console.log(res);

user_74863130

Use flatMap, Object.values and reduce. (Assuming that we want sum of all the existing key values).

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

const sum = array.flatMap(Object.values).reduce((sum, cur) => +cur + sum, 0);

console.log(sum)

user_78994770
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