✨ Feat: bind 함수 구현

assignment/src/bind.test.ts

@@ -0,0 +1,37 @@
+import { bind } from "./bind"
+
+describe("bind 함수 테스트", () => {
+  test("bind Basic", () => {
+    const users = { name: "d5ng" }
+
+    function getName(this: { name: string }) {
+      return `내 이름은 ${this.name}이에요!`
+    }
+
+    const bindingUser = bind(getName, users)
+    expect(bindingUser()).toBe("내 이름은 d5ng이에요!")
+  })
+
+  test("bind Partial", () => {
+    function greet(this: { name: string }, greeting: string, punctuation: string) {
+      return `${greeting}, ${this.name}${punctuation}`
+    }
+
+    const person = { name: "Alice" }
+    const greetAlice = bind(greet, person, "Hello")
+
+    expect(greetAlice("!")).toBe("Hello, Alice!")
+  })
+
+  test("생성자 함수 테스트", () => {
+    function Person(this: Record<string, any>, name: string) {
+      this.name = name
+    }
+
+    const BoundPerson = bind(Person, { name: "notUsed" })
+    const p = new BoundPerson("Tom")
+
+    expect(p.name).toBe("Tom")
+    expect(p instanceof Person).true
+  })
+})

assignment/src/bind.ts

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+type BindThis<T, U> = T extends (this: any, ...args: infer A) => infer R ? (this: U, ...args: A) => R : never
+
+type PartiallyBound<T, P extends any[]> = T extends (...args: [...P, ...infer Rest]) => infer R
+  ? (...args: Rest) => R
+  : never
+
+export function bind<T extends (this: any, ...args: any[]) => any, U, P extends any[]>(fn: T, thisArg: U, ...args: P) {
+  function boundFn(this: any, ...args2: any[]) {
+    const isInstnace = this instanceof boundFn
+
+    if (isInstnace) {
+      return fn.call(this, ...args, ...args2)
+    }
+
+    return fn.call(thisArg, ...args, ...args2) as PartiallyBound<BindThis<T, U>, P>
+  }
+
+  boundFn.prototype = Object.create(fn.prototype)
+
+  return boundFn
+}