An example of JavaScript generators.

generators.js

function *asyncThing1() {
  someAsyncFn(function(val) {
    yield val;
  });
}

function *asyncThing2(arg) {
  someOtherAsyncFn(arg, function(val) {
    yield val;
  });
}

function *asyncThing3(arg) {
  someOtherAgainAsyncFn(arg, function(val) {
    yield val;
  });
}

var result = asyncThing1().next(),
    result2 = asyncThing2(result).next(),
    result3 = asyncThing3(result2).next();