JavaScript での文字と文字列の重複

function characterOverlap(array1, array2) {
  let occurrence = {};

  let str = array1.concat(array2);

  // find the count of each character
  Array.from(str).forEach((char) => {
    let currentCount = occurrence[char] || 0;
    occurrence[char] = currentCount + 1;
  });

  // return the keys which is the individual character and join.
  const result = Object.keys(occurrence);

  return result.join("");
}

console.log(characterOverlap("computer", "circuitemtop"));
console.log(characterOverlap("frontend", "development"));
console.log(characterOverlap("mivrog", "gormiv"));
console.log(characterOverlap("praxet", "xetpar"));
console.log(characterOverlap("stone", "tones"));
console.log(characterOverlap("rescue", "secure"));

> computer
> frontedvlpm
> mivrog
> praxet
> stone
> rescu