js generate结合promise实现hello world

function* showHelloWorld() {
    let _s = '';
    _s += yield asyncFun(p1);
    _s += ' ';
    _s += yield asyncFun(p2);
    console.log(_s); //hello world
}

function asyncFun(cb_) {
    return new Promise(cb_)
}

function p1(cb_) {
    setTimeout(() => {
        cb_('hello');
    }, 1000);
}

function p2(cb_) {
    setTimeout(() => {
        cb_('world');
    }, 1000);
}

function forof(it_, data_) {
    const _obj = it_.next(data_);
    if (!_obj.done) {
        _obj.value.then(res_ => forof(it_, res_));
    }
}

forof(showHelloWorld());

该代码将在1s后将字符串改为hello

将在2s后将字符串改为hello world