Compare one array with a nested array and push value into a new array in Javascript

Question

I have 2 arrays

const arrayOne = [
 {id: '110'},
 {id: '202'},
 {id: '259'}
];

const arrayTwo = [
 {data: [{value: 'Alpha', id: '001'}]},
 {data: [{value: 'Bravo', id: '202'}]},
 {data: [{value: 'Charlie', id: '752'}]},
 {data: [{value: 'Delta', id: '202'}, {value: 'Sierra', id: '110'}]},
 {data: [{value: 'Echo', id: '937'}]}
];

I need to create a new array comparing arrayOne[idx].id with arrayTwo[idx].data[idx2].id

Upon match, I need to create an array pushing value or the entire matching object into a new array.

In this example, desired result should be newArray = ['Bravo', 'Delta', 'Sierra']

What I have tried:

let result = arrayOne.map(el => {
  let found = arrayTwo.find(f => f.data.at(0)?.id == el.id)?.data.at(0)?.value;
  return { id: el.id, value: found ?? null};
});

const result = arrayTwo
  .map(obj => obj.data[0])
  .map(obj => (arrayOne.find(v => v.id === obj.id) && obj.value))

arrayOne.map(item => ({
   ...item,
   result: arrayTwo.filter(itemTwo => item.data.map(x => x.id).includes(itemTwo.id))
}));

Answer 1

You're only checking the first index:

let found = arrayTwo.find(f => f.data.at(0)?.id == el.id)?.data.at(0)?.value;

If the first index doesn't match, but further indicies do, they won't be found.

I think you're overcomplicating things a bit. Make a Set of the IDs to find, then just iterate over each .data array, pushing the object to the output array if the ID matches.

const arrayOne=[{id:"110"},{id:"202"},{id:"259"}],arrayTwo=[{data:[{value:"Alpha",id:"001"}]},{data:[{value:"Bravo",id:"202"}]},{data:[{value:"Charlie",id:"752"}]},{data:[{value:"Delta",id:"202"},{value:"Sierra",id:"110"}]},{data:[{value:"Echo",id:"937"}]}];

const idsToFind = new Set(arrayOne.map(({ id }) => id));
const output = [];
for (const { data } of arrayTwo) {
  for (const obj of data) {
    if (idsToFind.has(obj.id)) output.push(obj.value);
  }
}
console.log(output);

If you prefer a less imperative approach:

const arrayOne=[{id:"110"},{id:"202"},{id:"259"}],arrayTwo=[{data:[{value:"Alpha",id:"001"}]},{data:[{value:"Bravo",id:"202"}]},{data:[{value:"Charlie",id:"752"}]},{data:[{value:"Delta",id:"202"},{value:"Sierra",id:"110"}]},{data:[{value:"Echo",id:"937"}]}];

const idsToFind = new Set(arrayOne.map(({ id }) => id));
const output = arrayTwo
  .flatMap(({ data }) => data.filter(
    obj => idsToFind.has(obj.id)
  ))
  .map(obj => obj.value);
console.log(output);