reduce: sum of lengths doesn't produce expected result

Question

I am trying to access the key 'children' inside of these nested arrays listed below. I want a total count of how many children there are. I am rather new to coding and I've been trying some things out but have not been able to figure the problem. any help?

also, I want to use the reduce method to accomplish this task thanks!

const characters = [
  {
    name: 'Eddard',
    spouse: 'Catelyn',
    children: ['Robb', 'Sansa', 'Arya', 'Bran', 'Rickon'],
    house: 'Stark',
  },
  {
    name: 'Jon',
    spouse: 'Lysa',
    children: ['Robin'],
    house: 'Arryn',
  },
  {
    name: 'Cersei',
    spouse: 'Robert',
    children: ['Joffrey', 'Myrcella', 'Tommen'],
    house: 'Lannister',
  },
  {
    name: 'Daenarys',
    spouse: 'Khal Drogo',
    children: ['Drogon', 'Rhaegal', 'Viserion'],
    house: 'Targaryen',
  },
  {
    name: 'Mace',
    spouse: 'Alerie',
    children: ['Margaery', 'Loras'],
    house: 'Tyrell',
  },
  {
    name: 'Sansa',
    spouse: 'Tyrion',
    house: 'Stark',
  },
  {
    name: 'Jon',
    spouse: null,
    house: 'Snow',
  },
];

const countNumberOfChildren = (arr) => {
  const selectChildren = arr.reduce((acc, c)=>{
   console.log('this is c', c)
   console.log('this is acc', acc)
   acc + c.children.length()
   console.log('this is acc2', acc)

  return acc
  }, 0)
  console.log(selectChildren) 
};

countNumberOfChildren(characters)

Answer 1

The issue is that acc + c.children.length() does not change the acc variable and that .length is not a function, it is a property. Also, so elements might not have a .children property.

You can condense that entire .reduce() call into one line and use optional chaining and null coalescing to handle elements that don't have a .children array like this:

const characters=[{name:'Eddard',spouse:'Catelyn',children:['Robb','Sansa','Arya','Bran','Rickon'],house:'Stark'},{name:'Jon',spouse:'Lysa',children:['Robin'],house:'Arryn'},{name:'Cersei',spouse:'Robert',children:['Joffrey','Myrcella','Tommen'],house:'Lannister'},{name:'Daenarys',spouse:'Khal Drogo',children:['Drogon','Rhaegal','Viserion'],house:'Targaryen'},{name:'Mace',spouse:'Alerie',children:['Margaery','Loras'],house:'Tyrell'},{name:'Sansa',spouse:'Tyrion',house:'Stark'},{name:'Jon',spouse:null,house:'Snow'}];


const numChildren = characters.reduce((acc, curr) => acc + (curr.children?.length ?? 0), 0);
console.log(numChildren);