lowercase the first letter of every key

lowercaseFirstLetter.js

// params = (accumulator, entry, index, object), where entry = [key, value]
const entriesReducer = (acc, [key, value]) => {
      const firstLetter = value.charAt(0).toLowerCase()
      const rest = value.slice(1)
      acc[key] = `${firstLetter}${rest}`
      return acc
    }

// accepts an object, returns an object
const lowerCaseAllValues = (obj) => {
  return Object.entries(obj).reduce(reducer, {})
}

const testCase = {
  one: 'One',
  two: 'TwoTwo'
}
const expected = {
  one: 'one',
  two: 'twoTwo'
}
const result = lowerCaseAllValues(testCase)

console.assert(result, expected)