yield_in_yield.js

function *foo() {
  yield 1;
  yield 2;
  yield 3;
}

function *boo() {
  yield 4;
  yield 5;
  yield 6;
}

function *assoc() {
  yield *foo();
  yield *boo();
}

var it = assoc();

for (let v of assoc() ){
  console.log(v);
}