each_huich.js

const noop = () => {};

const once = (fn) => {
  let called = false;

  return (...args) => {
    if (called) return;
    called = true;
    fn(...args);
  };
};

const each = (coll, iteratee, callback = noop) => {
  const oncedCallback = once(callback);
  if (coll.length === 0) {
    callback(null);
    return;
  }
  let completed = 0;
  const cbEach = err => {
    if (err) {
      oncedCallback(err);
      return;
    }
    completed++;
    if (completed === coll.length) {
      oncedCallback(null);
    }
  };
  coll.forEach(item => iteratee(item, cbEach));
};