main.js

const unitNames = {
  0: 'ZERO',
  1: 'ONE',
  2: 'TWO',
  3: 'THREE',
  4: 'FOUR',
  5: 'FIVE',
  6: 'SIX',
  7: 'SEVEN',
  8: 'EIGHT',
  9: 'NINE',
} as Record<number, string>

const troubledTeens = {
  11: 'ELEVEN',
  12: 'TWELVE',
  13: 'THIRTEEN',
  14: 'FOURTEEN',
  15: 'FIFTEEN',
  16: 'SIXTEEN',
  17: 'SEVENTEEN',
  18: 'EIGHTEEN',
  19: 'NINETEEN',
} as Record<number, string>

const tensNames = {
  10: 'TEN',
  20: 'TWENTY',
  30: 'THIRTY',
  40: 'FOURTY',
  50: 'FIFTY',
  60: 'SIXTY',
  70: 'SEVENTY',
  80: 'EIGHTY',
  90: 'NINETY',
} as Record<number, string>

const chequeLike = (input: number): string => {
  const inputString = input.toString()
  const digits = inputString.length

  if (digits === 3) {
    const hunderedName = unitNames[inputString[0]]
    const lastTwoDigits = Number(inputString.substring(1, 3))

    if (lastTwoDigits === 0) {
      return `${hunderedName} HUNDRED`
    }

    return `${hunderedName} HUNDRED AND ${belowHundred(lastTwoDigits)}`
  }

  return belowHundred(input)
}

const belowHundred = (input: number): string => {
  const inputString = input.toString()
  const digits = inputString.length

  if (digits === 2) {
    if (inputString[digits - 1] !== '0') {
      if (inputString[0] === '1') {
        return troubledTeens[input]
      }

      return (
        tensNames[Number(inputString[0]) * 10] +
        ' ' +
        unitNames[Number(inputString[1])]
      )
    }
    return tensNames[input]
  }

  return unitNames[input]
}

export { chequeLike }

main.spec.js

import { chequeLike } from './main'

// 2 digit numbers
// 10 should return “ten”
// 14 should return “fourteen”
// 20 should return “twenty”
// 21 should return “twenty-one”
// 56 should return “fifty-six”

describe('Cheque', () => {
  it.each`
    number | result
    ${0}   | ${'ZERO'}
    ${1}   | ${'ONE'}
    ${2}   | ${'TWO'}
    ${3}   | ${'THREE'}
    ${4}   | ${'FOUR'}
    ${5}   | ${'FIVE'}
    ${6}   | ${'SIX'}
    ${7}   | ${'SEVEN'}
    ${8}   | ${'EIGHT'}
    ${9}   | ${'NINE'}
    ${10}  | ${'TEN'}
    ${11}  | ${'ELEVEN'}
    ${12}  | ${'TWELVE'}
    ${13}  | ${'THIRTEEN'}
    ${14}  | ${'FOURTEEN'}
    ${15}  | ${'FIFTEEN'}
    ${16}  | ${'SIXTEEN'}
    ${17}  | ${'SEVENTEEN'}
    ${18}  | ${'EIGHTEEN'}
    ${19}  | ${'NINETEEN'}
    ${20}  | ${'TWENTY'}
    ${21}  | ${'TWENTY ONE'}
    ${30}  | ${'THIRTY'}
    ${40}  | ${'FOURTY'}
    ${50}  | ${'FIFTY'}
    ${60}  | ${'SIXTY'}
    ${70}  | ${'SEVENTY'}
    ${80}  | ${'EIGHTY'}
    ${88}  | ${'EIGHTY EIGHT'}
    ${90}  | ${'NINETY'}
    ${99}  | ${'NINETY NINE'}
    ${100} | ${'ONE HUNDRED'}
    ${132} | ${'ONE HUNDRED AND THIRTY TWO'}
    ${200} | ${'TWO HUNDRED'}
    ${999} | ${'NINE HUNDRED AND NINETY NINE'}
  `('should return $result when passed $number', ({ number, result }) => {
    expect(chequeLike(number)).toEqual(result)
  })
})