ES7: Executes functions asynchronously using promises and generators.

promise4.js

//invokes segments of an asynchronus function
function asyncF(generator) {
  try {
      var steps = generator(); // function to exec by segments
      return iterate(steps.next());
  } catch(e) {
     return Promise.reject(e); // rejects iteration
  }
  function iterate({value, done}) { // arg has value of prev iteration
       if (done) return Promise.resolve(value); // resolves all pending promises
       // make sure we have a promise and when resolved do another iteration
       // or iterator.throw rejects all pending promises
       return Promise.resolve(value).then( v => iterate(steps.next(v))).catch(e => steps.throw(e)); 
  }
}

promise = v => (new Promise(r => setTimeout( x => r(v), ((Math.random() * (10 - 1)) + 1 | 0) * 1000)));
console.log('print first');
asyncF(function* () {
    console.log(new Date(), yield promise(1)); //awaits for promise to resolve without blocking JS
    console.log(new Date(), yield promise(2));
    console.log(new Date(), yield promise(3));
    console.log(new Date(), yield promise(4));
    console.log(new Date(), yield promise(5));
    console.log(new Date(), yield promise(6));
    return 'last';
}).then(v => console.log(v), e => console.log(e)); //this prints 'last' or error
console.log('print second'); //executes immediatly since asyncFunc does not block JS

//or a compac version using a loop
asyncF(function* () {
    for(var i=1; i<6; i++){
    	console.log(new Date(), yield promise(i))
    }
});

//or using a map to execute all promises in parallel!
asyncF(function* () {
   for (var p of [1,2,3,4,5,6].map(promise)){
     console.log(new Date(), yield p)
   }
});

inspired by: https://jakearchibald.com/2014/es7-async-functions/

Refined with: http://exploringjs.com/es6/ch_generators.html#sec_co-library

//exec segments in a loop
asyncF(function* () {
for(var i=1; i<4; i++){
console.log( yield promise(i) ); //halts loop
console.log( yield promise(++i) ); //continues loop
}
console.log("done", i) //exec last
});

//Example:

function* (){
var customers = yield getCustomers('http://api.mycompany.com/customer'); //stops till customers is ready
var policies = customers.map(getPolicies); //gets all policies in parallel
for (policy in policies){
printReport(customers, yield policy); //prints policies sequencially
}
return 'done';
}