https://nagyadam2092.blogspot.hu/2016/07/demistfying-co.html

magic.js

magic(function*() {
    const uri = 'http://date.jsontest.com/';
    const response = yield fetch(uri);
    const date = yield response.json();
    const time = date.time;
    console.log('time: ', time);
});

function magic(generator) {
    const iterator = generator();
    const iteration = iterator.next();
    console.log('iteration: ', iteration);
    const promise = iteration.value;
    promise.then(response => {
        console.log('response: ', response);
        const anotherIterator = iterator.next(response);
        const anotherPromise = anotherIterator.value;
        anotherPromise.then(date=> iterator.next(date));
    });
}