Why does the .next generator need setTimeout?

Question

I am experimenting with ES6 generator functions and output operators, Example .

function run(generator) {
  var itr = generator(resume);

  function resume(callbackValue) {
    itr.next(callbackValue);
  }
  itr.next();
}

function* main(resume) {
  var result1 = yield add(1, resume);
  var data1 = result1;
  console.log("add 1 = ", data1)
  var data2 = yield add(1, resume);
  console.log("add 1 = ", data2);
  var data3 = yield add(data1, resume);
  console.log("add data1 =", data3);
  console.log("total is ", data1 + data2 + data3);
}

function add(num, resume) {
  setTimeout(function() {
    resume(num + 1);
  }, 0);
}

run(main);

I plan to use the output as a flow control for asynchronous REST calls, where the request will be called next after the answer, but for now I just use a simple add. It works as planned, which is interesting, but renewal will only work in setTimeout, and I'm not sure why. If it is simple:

function add (num, resume) {
    resume(num + 1);
} 

the interpreter gives me "The generator is already running."

No need to be a real wait during a timeout, and I also tried the self invoking function, but that didn't help. Why do I itr.next()need a timeout?

Answer 1

, resume, yield . itr.next , itr.next, . , , run:

function run(generator) {
  var itr = generator(resume);

  function resume(callbackValue) {
    setTimeout(function(){
      itr.next(callbackValue);
    }, 0);
  }
  itr.next();
}

, .