try out ES2015 Generator - yield vs. yield* (delegation)

es6-generator-yield.js

// `yield*`: yield delegation
function* gen1() {
  yield gen2();
  yield* gen2();
  yield [3, 4];
  yield* [3, 4];
}

function* gen2() {
  yield 1;
  yield 2;
}

let iter = gen1();
for (let value of iter) {
  console.log(value);
}
// output:
// {}
// 1
// 2
// [3, 4]
// 3
// 4