> For the complete documentation index, see [llms.txt](https://ahnheejong.gitbook.io/ts-for-jsdev/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ahnheejong.gitbook.io/ts-for-jsdev/02-ecmascript/element-enumeration/iterator-protocol.md).

# 2.5.3 이터레이터 프로토콜

객체가 특정 조건을 만족하는 `next()` 메소드를 가질 때, 이러한 객체를 이터레이터(반복자, Iterator)라 부른다. 이 때, `next()` 메소드는 해당 객체의 요소들을 어떤 방식과 어떤 순서로 순회할지를 정의하며, 호출 될 때마다 아래 두 가지 값을 담은 객체를 반환해야 한다.

* 순회가 끝났는지를 나타내는 불리언 값인 `done`
* (`done === false` 일시) 이번 원소의 값인 `value`

아래 코드는 객체를 받아 객체의 요소를 순회하기 위한 이터레이터를 생성하고, 실제로 해당 이터레이터를 순회하는 간단한 예시다.

```javascript
function makeIterator(array) {
    var nextIndex = 0;
    return {
       next: function() {
           return nextIndex < array.length
               ? { value: array[nextIndex++], done: false } 
               : { done: true};
       }
    };
}
const iter = makeIterator([1, 2, 3]);
iter.next(); // { value: 1, done: false }
iter.next(); // { value: 2, done: false }
iter.next(); // { value: 3, done: false }
iter.next(); // { done: true }
```


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