asynchronous - Implementing coroutine control flow in JavaScript

Question

The following implements a control flow wrapper co enabling asynchronous code to be delineated only by the yield keyword.

Is this basically what async/await does under the hood in ESwhatever?

co(function*() {
    console.log('...');
    yield one();
    console.log('...');
    yield two();
})


function co(gFn) {
    var g = gFn();

    return Promise.resolve()
        .then(go);

    function go() {        
        var result = g.next();
        if(result.done) {
            return;
        }
        if(isPromise(result.value)) {
            return result.value.then(go); // Promises block until resolution.
        }
        return Promise.resolve(result);
    }    
}

function isPromise(o) {
    return o instanceof Promise;
}

function one() {
    return new Promise(resolve => setTimeout(() => (console.log('one'), resolve()), 1000));
}

function two() {
    return new Promise(resolve => setTimeout(() => (console.log('two'), resolve()), 1000));
}

Answer 1

Is this basically what async/await does under the hood in ESwhatever?

Not really. It's a different approach for doing sorta the same thing. What async/await turn into is more like

async function foo() {
  const bar = await Bar();
  bar++;
  const baz = await Baz(bar);
  return baz;
}

becomes

function foo() {
  return Bar()
    .then(bar => {
      bar++;
      return Baz(bar)
        .then(baz => {
          return baz;
        });
    });
}