Factory Functions & Singleton Pattern

What design pattern does this factory function implement?

function createIterator(array) {
  let nextIndex = 0;
  
  return {
    next() {
      if (nextIndex < array.length) {
        return { value: array[nextIndex++], done: false };
      } else {
        return { done: true };
      }
    },
    hasNext() {
      return nextIndex < array.length;
    },
    reset() {
      nextIndex = 0;
    }
  };
}

Observer pattern
Iterator pattern
This factory function implements the Iterator pattern: 1) It creates an object that provides sequential access to collection elements, 2) It maintains internal state to track the current position, 3) It provides a standard interface (next(), hasNext()) for iteration, 4) It abstracts away collection traversal details, 5) It allows for custom iteration behavior like reset(), 6) This pattern is useful for creating custom iteration logic over collections or data structures.
Command pattern
Mediator pattern

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