A function that creates a generator over a subset of a specified iterable using a condition

subIterable.js

const filter = function* (iterable, cond) {
  const iterator = iterable[Symbol.iterator]();
  let cursor = iterator.next();
  do {
    const {value} = cursor;
    if (cond(value)) {
      yield value;
    }
  } while (!(cursor = iterator.next()).done);
};


export {filter};

Usage:

const arr = [1, 2, 3, 4, 5, 6];

console.log([...filter(arr, x => x % 2 === 0)]); // [ 2, 4, 6 ]
console.log([...filter(arr, x => x % 2 === 1)]); // [ 1, 3, 5 ]

Note that this function also works for "infinite" iterables.