Promises + generators

gistfile1.js

async(function*() {
    console.log('start');
    yield asyncFunction();
    var value = yield asyncFunction();
    console.log('value', value);
});

function asyncFunction() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log('lalala');
            resolve('123');
        }, 5000);
    });
}

function async(genFunc) {
    var gen = genFunc();
    function step(value) {
        var next = gen.next(value);
        var promise = next.value;
        return promise
            .then((v) => {
                if (!next.done) {
                    step(v);
                }
            })
            .catch((e) => gen.throw(e));
    }

    return step();
}