function* wrap() {
    yield sleep(1000);
    yield sleep(2000);
}

function sleep(time) {
    return function(done) {
        setTimeout(function() {
            console.log('sleep ' + time + 'ms');
            done(null, time);
        }, time);
    }
}
function co(generator, err, res) {
    var ret = generator.next(res);
    if (ret.done) return;
    ret.value(function(err, res) {
       co(generator, err, res); 
    });
}

co(wrap());

function* wrap2() {
    yield sleep2.call(this, 4000);
    yield sleep2.call(this, 1000);
}

function sleep2(time) {
    setTimeout(function() {
        console.log('sleep ' + time + 'ms');
        this.next();
    }.bind(this), time)
}

function co2(generator) {
    new generator().next();
}

co2(wrap2);