어린왕자와 여우

Operator delete is unexpectedly slow!

Delete is the only true way to remove object’s properties without any leftovers, but it works ~ 100 times slower, compared to it’s “alternative”, setting object[key] = undefined. 

Use setting to undefined, when you care about performance. It can give a serious boost to your code. The key remains on its place in the hashmap, only the value is replaced with undefined. Understand, that for..in loop will still iterate over that key. There is no way to force garbage collection in JavaScript, and you don’t really need to. x.y = null; and delete x.y; both eliminate x’s reference to the former value of y. 

The value will be garbage collected when necessary. The only time I can think of where you would prefer delete is if you were going to enumerate over the properties of x. If you null out a property, it is still considered ‘set’ on the object and will be enumerated.

http://stackoverflow.com/a/21735614
http://stackoverflow.com/questions/1947995
http://bertanguven.com/preventing-memory-leaks-in-javascript-null-vs-delete/
http://perfectionkills.com/understanding-delete/


요약
- delete 는 단순히 객체와 속성과의 연결을 끊을 뿐 실제로 메모리에서 제거하는 것은 아니다.

- delete 하고 싶은 delete 연산자를 사용하기보다 값을 null 이나 undefined 로 설정하는것을 추천한다.

- 단, 이 경우 hashmap 에서 key 가 삭제되는 것은 아니라서 for-in loop 을 사용하거나, hasOwnProperty() 같이 key 의 존재를 체크하는 경우에는 key가 드러나긴 할거다. 하지만 value === undefined 같은 식으로 체크하는 경우는 문제없을거다.

- 자바스크립트에서 gc 를 강제로 트리거 할 방법은 없고 브라우저가 필요한 tick 에 알아서 한다.

성능측정
http://jindo.dev.naver.com/jsMatch/index.html?d=192&openResult=1

출처 : https://medium.com/@laziel/javascript-%EA%B0%9D%EC%B2%B4%EC%9D%98-%EC%86%8D%EC%84%B1%EC%9D%84-%EC%A0%9C%EA%B1%B0%ED%95%A0-%EB%95%8C-delete-%EC%97%B0%EC%82%B0%EC%9E%90%EB%B3%B4%EB%8B%A4-undefined-%EB%82%98-null-%EA%B0%92%EC%9C%BC%EB%A1%9C-%EB%A7%8C%EB%93%9C%EB%8A%94-%EA%B2%83%EC%9D%B4-%EB%82%AB%EB%8B%A4-2db597f64514#.c7cb0m7v7