docs(Extract): Add Extract documentation

docs/ko/reference/built-in/Extract.md

@@ -1 +1,77 @@
-# Extract
+# Record\<Type, Union>
+
+:::info
+`Extract<Type, Union>`은 TypeScript 2.8 이상에서 사용할 수 있는 내장 유틸리티 타입이에요. 자세한 내용은 [타입스크립트 핸드북](https://www.typescriptlang.org/docs/handbook/utility-types.html#extracttype-union)과 [릴리즈 노트](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html#predefined-conditional-types)를 참고해주세요.
+:::
+
+## 개요
+
+`Extract<Type, Union>`은 `Union`에 할당할 수 있는 모든 유니온 멤버를 `Type`에서 추출하여 타입을 구성하는 TypeScript 내장된 유틸리티 타입이에요.
+
+## 문법
+
+```ts
+type Extract<T, U> = T extends U ? T : never;
+```
+
+- **Type (T)**: 유니온 멤버를 추출하고자 하는 타입을 나타내요.
+- **Union (U)**: `Type`에서 추출하고자 하는 타입을 나타내요.
+
+## 예제
+
+#### 예제 #1
+
+```ts
+type User = 'admin' | 'editor' | 'viewer';
+
+type PrivilegedUser = Extract<User, 'admin' | 'editor'>; // 'admin' | 'editor'
+```
+
+#### 예제 #2
+
+```ts
+type OnlyFunction = Extract<string | number | symbol | (() => void), Function>; // () => void
+```
+
+#### 예제 #3
+
+```ts
+type Primitive = string | number | boolean | bigint | symbol | null | undefined;
+
+type NonPrimitive<T> = Extract<T, Primitive>;
+
+type NonPrimitiveTypes = NonPrimitive<string | number | object>; // object
+```
+
+#### 예제 #4
+
+```ts
+declare function uniqueId(): number;
+
+const ID = Symbol('ID');
+
+interface Product {
+    [ID]: number;
+    name: string;
+    price: number;
+}
+
+type ProductUpdatableKeys = Extract<keyof Product, string>;
+
+function updateProduct <
+    Obj extends Product,
+    Key extends ProductUpdatableKeys,
+    Value extends Obj[Key]
+> (obj: Obj, key: Key, value: Value) {
+    obj[key] = value;
+}
+
+const product: Product = {
+    [ID]: uniqueId(),
+    name: 'box',
+    price: 5000
+}
+
+updateProduct(product, 'name', 'paper'); // ✅
+updateProduct(product ID, uniqueId()); // ❌
+```

docs/reference/built-in/Extract.md

@@ -1 +1,77 @@
-# Extract
+# Extract\<Type, Union>
+
+:::info
+The `Extract<Type, Union>` utility type is available starting from TypeScript version 2.8. For more information see in [TypeScript Handbook](https://www.typescriptlang.org/docs/handbook/utility-types.html#extracttype-union), [Release Note](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html#predefined-conditional-types).
+:::
+
+## Overview
+
+The `Extract<Type, Union>` is a built in utility type in TypeScript that constructs a type by extracting from `Type` all union members that are assignable to `Union`.
+
+## Syntax
+
+```ts
+type Extract<T, U> = T extends U ? T : never;
+```
+
+- **Type (T)**: This represents a type from which you want to extract union members.
+- **Union (U)**: This represents the members or types that you want to extract from the `Type`.
+
+## Examples
+
+#### Example #1
+
+```ts
+type User = 'admin' | 'editor' | 'viewer';
+
+type PrivilegedUser = Extract<User, 'admin' | 'editor'>; // 'admin' | 'editor'
+```
+
+#### Example #2
+
+```ts
+type OnlyFunction = Extract<string | number | symbol | (() => void), Function>; // () => void
+```
+
+#### Example #3
+
+```ts
+type Primitive = string | number | boolean | bigint | symbol | null | undefined;
+
+type NonPrimitive<T> = Extract<T, Primitive>;
+
+type NonPrimitiveTypes = NonPrimitive<string | number | object>; // object
+```
+
+#### Example #4
+
+```ts
+declare function uniqueId(): number;
+
+const ID = Symbol('ID');
+
+interface Product {
+    [ID]: number;
+    name: string;
+    price: number;
+}
+
+type ProductUpdatableKeys = Extract<keyof Product, string>;
+
+function updateProduct <
+    Obj extends Product,
+    Key extends ProductUpdatableKeys,
+    Value extends Obj[Key]
+> (obj: Obj, key: Key, value: Value) {
+    obj[key] = value;
+}
+
+const product: Product = {
+    [ID]: uniqueId(),
+    name: 'box',
+    price: 5000
+}
+
+updateProduct(product, 'name', 'paper'); // ✅
+updateProduct(product ID, uniqueId()); // ❌
+```