jaawerth's iterator concat (es6 generator-based)

iterator.concat.js

/* Concatenate iterators by wrapping them in a "parent" iterator.
 * When it's consumed, to the outside world it will appear as a single
 * iterator. Allows for easily-implemented lazy evaluation and immutable
 * transformations.
*/

import toIterator from './iterator';
import { isArray, isIterable, isIterator } from '../types';

function concat(...items) {
  // Flatten only a single argument
  if (items.length === 1) return _concat(items[0]);
  return _concat(toIterator(items));
}

// we hear you like iterators, so we made iterators for your iterators
function* _concat(iters) {
    let iter = iters.next();

    while ( !iter.done ) {
      yield* iterate(iter.value);
      iter = iters.next();
    }
}
// iterate the "member" iterators
function* iterate (iter) {
  var el = iter.next();

  while (!el.done) {
    yield el.value;
    el = iter.next();
  }
}

export default concat;