关于javascript:es6-async-函数的实现原理

自己有幸在《深刻了解 ES6》中看到如何通过自行封装生成器来执行异步工作，是它同步运行。
源码如下：

   function* queryInfo() {const res1 = yield new Promise((res, rej) => {res(200);
        });
        console.log({res1});
        try{const res2 = yield new Promise((res, rej) => {rej(403);
            });
            console.log({res2});
        }catch(e){console.log("res2 谬误:", e)
        }

        const res3 = yield new Promise((res, rej) => {res(304);
        });
        console.log({res3});
    }

    function run(gnFn) {
        // 创立迭代器
        const gn = gnFn();

        // 开启迭代
        let res = gn.next();

        (function step() {if (!res.done) {const promise = Promise.resolve(res.value);

                promise.then(value => {res = gn.next(value);
                    step();}).catch(e => {res = gn.throw(e);
                    step();})
            }
        })()}

    run(queryInfo); // {res1: 200} res2 谬误:403 {res3: 304}