Type safe pick function

pick.test.ts

import pick, { pickAndGetRest } from "./pick"

describe("pick util", () => {
  it("picks from an object", () => {
    const obj = {
      a: 1,
      b: 2,
      c: 3,
      foo: "bar",
      bar: "bah",
    }
    const picked = pick(obj, "a", "c", "bar")
    expect(picked).toEqual({
      a: 1,
      c: 3,
      bar: "bah",
    })
  })

  it("picks and gives the rest from an object", () => {
    const obj = {
      a: 1,
      b: 2,
      c: 3,
      foo: "bar",
      bar: "bah",
    }
    const [picked, rest] = pickAndGetRest(obj, "a", "c", "bar")
    expect(picked).toEqual({
      a: 1,
      c: 3,
      bar: "bah",
    })
    expect(rest).toEqual({
      b: 2,
      foo: "bar",
    })
  })
})

pick.ts

export const pick = <T extends {}>(obj: T, ...keys: (keyof T)[]) => {
  return pickAndGetRest(obj, ...keys)[0]
}

export const pickAndGetRest = <T extends {}, K extends keyof T>(obj: T, ...keys: K[]): [Pick<T, K>, Omit<T, K>] => {
  const picked: any = {}
  const rest: any = {}
  for (let key of Object.keys(obj)) {
    if (keys.includes(key as K)) {
      picked[key] = obj[key]
    } else {
      rest[key] = obj[key]
    }
  }
  return [picked, rest]
}

export default pick