Create an object instead of an array

reduce.js

const ABC = ["a", "b", "c"];

ABC.reduce((acc, key) => {
  acc[key] = `${key}!`;

  return acc;
}, Object.create(null));

ABC.reduce(
  (acc, key) => Object.assign(acc, { [key]: `${key}!` }),
  Object.create(null)
);

ABC.reduce(
  (acc, key) => ({
    ...acc,
    [key]: `${key}!`
  }),
  Object.create(null)
);

// { a: "a!", b: "b!", c: "c!" }