Data fetching it typescript

Fetcher.ts

type HttpMethod = 'GET' | 'POST' | 'PUT' | 'DELETE'

interface HeadersObject {
  [key : string] : string
}

interface FetcherResponse {
  data : object,
  headers : HeadersObject
}

export const request = async (
  method : HttpMethod,
  path : string,
  body : object = {}
) : Promise<FetcherResponse> => {
  const requestInit : RequestInit = {
    method: method,
    headers: defaultHeaders()
  }

  if (bodyAllowed(method)) {
    requestInit.body = JSON.stringify(body)
  }

  const response = await fetch(path, requestInit)
  const data = await response.json()
  const headers = unpackHeaders(response)

  return {data, headers}
}

const defaultHeaders = () : HeadersObject => {
  return {
    'Accept': 'application/json',
    'Content-Type': 'application/json',
  }
}

const unpackHeaders = (response : Response) : HeadersObject => {
  const entries = Array.from(response.headers.entries())
  return entries.reduce((acc : HeadersObject, [key, value]) => {
    acc[key] = value
    return acc
  }, {})
}

const bodyAllowed = (method : HttpMethod) : boolean =>
  ['POST', 'PUT'].includes(method)

SessionsProvider.ts

import {request} from './Fetcher'

interface LoginActionParams {
  email : string,
  password : string
}

export const loginAction = async (params : LoginActionParams) => {
  const {email, password} = params
  const {data, headers} = await request(
    'POST',
    'http://localhost:3001/api/v1/users/sign_in',
    {user: {email, password}}
  )

  return data
}