From fb78901f70d8becd267723b25fcdb901adc189fd Mon Sep 17 00:00:00 2001 From: unknown Date: Fri, 8 Nov 2019 10:22:07 +0900 Subject: [PATCH 1/2] =?UTF-8?q?#359=20[=ED=95=A8=EC=88=98=EC=9D=98=20proto?= =?UTF-8?q?type=20=ED=94=84=EB=A1=9C=ED=8D=BC=ED=8B=B0]=20=EA=B3=BC?= =?UTF-8?q?=EC=A0=9C1=20=EC=A0=95=EB=8B=B5=20=EB=B2=88=EC=97=AD?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- .../1-changing-prototype/solution.md | 44 ++++++++++++++----- 1 file changed, 34 insertions(+), 10 deletions(-) diff --git a/1-js/08-prototypes/02-function-prototype/1-changing-prototype/solution.md b/1-js/08-prototypes/02-function-prototype/1-changing-prototype/solution.md index ebbdf3a7c1..8e6c75c1f3 100644 --- a/1-js/08-prototypes/02-function-prototype/1-changing-prototype/solution.md +++ b/1-js/08-prototypes/02-function-prototype/1-changing-prototype/solution.md @@ -1,20 +1,44 @@ +`"constructor"` 프로퍼티에 제대로 된 값이 저장되어있다면 위와 같은 접근법이 가능합니다. -Answers: +기본 `"prototype"`를 변경하지 않았다면 아래 예시는 의도한 대로 동작합니다. -1. `true`. +```js run +function User(name) { + this.name = name; +} - The assignment to `Rabbit.prototype` sets up `[[Prototype]]` for new objects, but it does not affect the existing ones. +let user = new User('John'); +let user2 = new user.constructor('Pete'); -2. `false`. +alert( user2.name ); // Pete (잘 동작하네요!) +``` - Objects are assigned by reference. The object from `Rabbit.prototype` is not duplicated, it's still a single object referenced both by `Rabbit.prototype` and by the `[[Prototype]]` of `rabbit`. +`User.prototype.constructor == User`이기 때문에 위 예시는 제대로 동작합니다. - So when we change its content through one reference, it is visible through the other one. +그런데 누군가가 `User.prototype`를 덮어쓰고 `User`를 참조하는 `constructor`를 다시 만들어주는 걸 잊었다면 문제의 접근법은 실패합니다. -3. `true`. +예시: - All `delete` operations are applied directly to the object. Here `delete rabbit.eats` tries to remove `eats` property from `rabbit`, but it doesn't have it. So the operation won't have any effect. +```js run +function User(name) { + this.name = name; +} +*!* +User.prototype = {}; // (*) +*/!* -4. `undefined`. +let user = new User('John'); +let user2 = new user.constructor('Pete'); - The property `eats` is deleted from the prototype, it doesn't exist any more. +alert( user2.name ); // undefined +``` + +왜 `user2.name`이 `undefined`가 될까요? + +그 이유는 `new user.constructor('Pete')`가 아래와 같이 동작하기 때문입니다. + +1. `new user.constructor('Pete')`는 `user`에서 `constructor`를 찾는데 아무것도 찾지 못합니다. +2. 객체에서 원하는 프로퍼티를 찾지 못했기 때문에 프로토타입에서 검색을 시작합니다. `user`의 프로토타입은 `User.prototype`인데, `User.prototype`은 빈 객체입니다. +3. `User.prototype`은 일반 객체 `{}`이고, 일반 객체의 프로토타입은 `Object.prototype`입니다. `Object.prototype.constructor == Object`이므로 `Object`가 사용됩니다. + +결국에 `let user2 = new user.constructor('Pete');`는 `let user2 = new Object('Pete')`가 됩니다. 그런데 `Object`의 생성자는 인수를 무시하고 항상 빈 객체를 생성합니다. 따라서 `let user2 = new Object('Pete')`는 `let user2 = {}`와 같다고 생각할 수 있습니다. `user2.name`이 `undefined`인 이유가 여기에 있습니다. \ No newline at end of file From d1a6c942996ff3ad36eabf4e870083178281a740 Mon Sep 17 00:00:00 2001 From: unknown Date: Fri, 8 Nov 2019 11:11:44 +0900 Subject: [PATCH 2/2] =?UTF-8?q?#359[=ED=95=A8=EC=88=98=EC=9D=98=20prototyp?= =?UTF-8?q?e=ED=94=84=EB=A1=9C=ED=8D=BC=ED=8B=B0]=EA=B3=BC=EC=A0=9C1=20?= =?UTF-8?q?=EC=A0=95=EB=8B=B5=20=EB=B2=88=EC=97=AD?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- .../02-function-prototype/1-changing-prototype/solution.md | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/1-js/08-prototypes/02-function-prototype/1-changing-prototype/solution.md b/1-js/08-prototypes/02-function-prototype/1-changing-prototype/solution.md index 8e6c75c1f3..b73b6c9354 100644 --- a/1-js/08-prototypes/02-function-prototype/1-changing-prototype/solution.md +++ b/1-js/08-prototypes/02-function-prototype/1-changing-prototype/solution.md @@ -5,7 +5,7 @@ ```js run function User(name) { this.name = name; -} +}; let user = new User('John'); let user2 = new user.constructor('Pete'); @@ -22,7 +22,7 @@ alert( user2.name ); // Pete ( ```js run function User(name) { this.name = name; -} +}; *!* User.prototype = {}; // (*) */!*