Implement an iterable and make the iterators also iterable which leads to continuable iteration

1_iterable.js

class YourConstruct {
  constructor() {}
  
  // implement iterable protocol
  [Symbol.iterator]() {
    // return an iterator
    return {
      // the iterator is iterable!
      [Symbol.iterator]() {
        return this;
      }
      
      next() {
        // ...
        // return {value: any, done: boolean}
      }
    };
  }
}

2_continuable_iteration.js

let yourConstruct = new YourConstruct();
// ...
for (let v of yourConstruct) {
  // ...
}

let iterator = yourConstruct[Symbol.iterator]();
console.log(iterator[Symbol.iterator]() === iterator); // => true

for (let x of iterator) {
  console.log(x);
  break;
}
// continue iteration in another loop
for (let y of iterator) {
  console.log(y);
}

3_magic.md

The magic why it can continue the iteration in another loop instead of restarting the iteration each time is that: A single iterator instance is returned that is also iterable to iterate the construct.