Typescript: Create object with same keys but different values

Question

I have the following initial object

const initialValues = { name: 'Jon', email: '[email protected]' }

I would like to create an identical object except where all the values are boolean and default to false. Like so

const expected = { name: false, email: false }

I created the following function which does what I want

const expected = cloneWithDefaults<typeof initialValues>(initialValues)

function cloneWithDefaults<T>(values: T) {
  type U = { [K in keyof T]: boolean }
  const keys = Object.keys(values) as Array<keyof T>
  const partial: Partial<U> = keys.reduce<Partial<U>>((acc, cur) => {
    acc[cur] = false
    return acc
  }, {})
  const final = partial as U
  return final
}

I also created a second version which does not use reduce

function createCloneWithDefaultsV2<T extends { [key: string]: unknown }>(values: T) {
  type U = { [K in keyof T]: boolean }
  const keys = Object.keys(values) as Array<keyof U>
  const partial: Partial<U> = {}
  for (let k in keys) {
    partial[k] = false
  }
  const final = partial as U
  return final
}

I wonder if there is a better / more succinct way of doing this. In particular I would like to get rid of the two uses of as if possible.

In the v2 I wonder if there is any preference for unknown as opposed to any.

Answer 1

Here's how I would write it:

    function cloneWithDefaults<T>(values: T) {
        return <{[key in keyof T]: boolean}> Object.entries(values).reduce((p, [k, v]) => Object.assign(p, { [k]: false }), {});
    }
    const initialValues = { name: 'Jon', email: '[email protected]' };
    const expected = cloneWithDefaults(initialValues);

Due to the reduce() call, I don't see an option without a cast. (Either from partial or from any.) Note that Object.entries() requires downlevelIteration ts compiler option to be true (https://www.typescriptlang.org/docs/handbook/compiler-options.html).