const highTechWorkers = ['20', '25', '41', '9'];
const reducer = ()

const result = highTechWorkers.flatMap((worker) => {
  const age = parseInt(worker);
  if (age < 35) {
    return [`age ${worker} is OK`]; // Keep it, in array
  } else {
    return []; // Delete it!
  }
});

console.log(result); 
//["age 20 is OK", "age 25 is OK", "age 9 is OK"]

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