asyncgen.js

function foo(x, y) {
  ajax(
    "http://some.url/?x=" + x + "&y=" + y,
    function(err, data) {
      if (err) {
        it.throw(err);
      } else {
        it.next(data);
      }
    }
  );
}

function* main() {
  try {
    var text =
      yield foo(11, 31);
    console.log(text);
  } catch (err) {
    console.error(err);
  }
}

var it = main();

it.next();