async patterns with generators and promises

function callAsync(fn) {
    // get iterator
    var iterator = fn();

    // used as a callback to currently yielded functions 
    function next() {
        // get next function
        var current = iterator.next();

        // recursion exit condition
        if (current.done) { return; }

        // call async function and pass next() as aa callback so it will ask the iterator to yield next when callback is called
        var promise = current.value;

        promise.then(next);
    }

    // initialise recursion
    next();
}

// delay function as a simple example of something that returns promise
function delay(timeout) {
    return new Promise((resolve, reject) => setTimeout(resolve, timeout));
}

callAsync(function* () {
    yield delay(1000);
    console.log('waited for 1 sec');

    yield delay(2000);
    console.log('waited for 2 sec');
});