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to Phone Number in the TypeScript Track

Published at Sep 27 2019 · 0 comments
Test suite

Clean up user-entered phone numbers so that they can be sent SMS messages.

The North American Numbering Plan (NANP) is a telephone numbering system used by many countries in North America like the United States, Canada or Bermuda. All NANP-countries share the same international country code: 1.

NANP numbers are ten-digit numbers consisting of a three-digit Numbering Plan Area code, commonly known as area code, followed by a seven-digit local number. The first three digits of the local number represent the exchange code, followed by the unique four-digit number which is the subscriber number.

The format is usually represented as


where N is any digit from 2 through 9 and X is any digit from 0 through 9.

Your task is to clean up differently formatted telephone numbers by removing punctuation and the country code (1) if present.

For example, the inputs

  • +1 (613)-995-0253
  • 613-995-0253
  • 1 613 995 0253
  • 613.995.0253

should all produce the output


Note: As this exercise only deals with telephone numbers used in NANP-countries, only 1 is considered a valid country code.


Go through the setup instructions for TypeScript to install the necessary dependencies:



Install assignment dependencies:

$ yarn install

Making the test suite pass

Execute the tests with:

$ yarn test

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by changing xit to it.


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Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


import PhoneNumber from './phone-number'

describe('PhoneNumber()', () => {

  it('cleans the number', () => {
    const phone = new PhoneNumber('(223) 456-7890')

  xit('cleans numbers with dots', () => {
    const phone = new PhoneNumber('223.456.7890')

  xit('cleans numbers with multiple spaces', () => {
    const phone = new PhoneNumber('223 456   7890   ')

  xit('invalid when 9 digits', () => {
    const phone = new PhoneNumber('123456789')

  xit('invalid when 11 digits', () => {
    const phone = new PhoneNumber('21234567890')

  xit('valid when 11 digits and starting with 1', () => {
    const phone = new PhoneNumber('11234567890')

  xit('invalid when 12 digits', () => {
    const phone = new PhoneNumber('321234567890')

  xit('invalid with letters', () => {
    const phone = new PhoneNumber('123-abc-7890')

  xit('invalid with punctuations', () => {
    const phone = new PhoneNumber('123-@:!-7890')

  xit('invalid with right number of digits but letters mixed in', () => {
    const phone = new PhoneNumber('1a2b3c4d5e6f7g8h9i0j')

export default class PhoneNumber {
    constructor(private num: string) {}

    number() {
        let match = this.num.match(/^1?\(?(\d{3})\)?\.?\s*(\d{3})\.?-?\s*(\d{4})\s*$/);
        return match !== null ? `${match[1]}${match[2]}${match[3]}` : undefined

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