cursor.js

const createCursor = (directions, onMove) => {
  const dirKeys = Object.keys(directions);
  const cursor = {};

  let location = 0;

  cursor.max = 1000;

  cursor.get = () => location;

  cursor.set = nextLocation => {
    if (onMove) onMove(nextLocation, location);
    location = nextLocation;
    return cursor;
  };

  Object.keys(directions).forEach(key => {
    cursor[key] = predicate => {
      let nextLocation = location;
      if (predicate) {
        let i = 0;
        do {
          nextLocation = directions[key](nextLocation);
          if (i++ > cursor.max) {
            throw new Error('cursor exceeded max: ' + cursor.max);
          }
        } while (!predicate(nextLocation));
      } else {
        nextLocation = directions[key](nextLocation);
      }
      return cursor.set(nextLocation);
    };
  });

  return cursor;
};

const list = ['A', 'B', 'C'];

const listCursor = createCursor(
  {
    next: idx => idx + 1,
    prev: idx => idx - 1,
  },
  location => {
    console.log(location);
  }
);

console.log(3 % 3);
const by3 = v => v % 3 === 0;

listCursor
  .next()
  .next()
  .next()
  .next(by3)
  .next(by3)
  .prev()
  .set(26)
  .prev(by3)
  .prev(by3)
  .next(by3);