One-time iterator operation in JavaScript

Each iterator can participate in the loop only once. This is a bit unexpected, but logical - after all, the passed iterator sets its done to false, which means it can no longer be iterated over.

Let's make sure of this. Let's have the following generator:

javascriptfunction *func() {
  yield 1;
  yield 2;
  yield 3;
}

Let's make an iterator:

javascriptlet iter = func();

And iterate over the iterator in one loop:

javascriptfor (let elem of iter) {
  console.log(elem); // 1, 2, 3
}

And now iterate over the iterator in two loops:

javascriptfor (let elem of iter) {
  console.log(elem); // 1, 2, 3
}
for (let elem of iter) {
  console.log(elem); // doesn't work
}

To solve the problem, you need to create your own iterator for each new loop:

javascriptlet iter1 = func();
for (let elem of iter1) {
  console.log(elem); // 1, 2, 3
}

let iter2 = func();
for (let elem of iter2) {
  console.log(elem); // 1, 2, 3
}

We can simplify:

javascriptfor (let elem of func()) {
  console.log(elem); // 1, 2, 3
}

for (let elem of func()) {
  console.log(elem); // 1, 2, 3
}

javascriptfunction *func() {
  for (let i = 1; i <= 3; i++) {
    yield i;
  }
}

let elems = func();

for (let elem of elems) {
  console.log(elem);
}
for (let elem of elems) {
  console.log(elem);
}