ES6-yiel

function *fn() {
  console.log('a');

  let tmp = yield;

  console.log('b');
  console.log(tmp);
}

const gen = fn();

// gen.next = () => { console.log('a'); }
gen.next(12); // generator 的第一个next 的参数没有意义

// gen.next = () => { let a = 5; console.log('b'); console.log(tmp);  }
gen.next(5);