getQueryParams.js

import { fromPairs, map, path, pipe, split, tail } from 'ramda'

const removeEmptyQuery = filter(complement(isNil))

const getQueryParams = pipe(
  path(['location', 'search']),
  tail,
  split('&'),
  map(split('=')),
  fromPairs,
  removeEmptyQuery,
  map(decodeURI)
);

export default getQueryParams

script.js

import getQueryParams from './getQueryParams'

const window = {
  location: {
    search: '?first=the%20first%20one&second=the%20second%20one'
  }
}

getQueryParams(window)
// {"first": "the first one", "second": "the second one"}

try it out