phone-number.js

function hasAlphaChars(original, cleaned) {
  return !(original.match(/[a-z]/gi)) ? cleaned : null;
}

function hasIncorrectLength(original, cleaned) {
  return (cleaned && cleaned.length == 10) ? cleaned : null;
}

function clear(original) {
  let cleaned = original.replace(/[^0-9]/g, '');

  if (cleaned.length === 11 && cleaned[0] === '1') {
    cleaned = cleaned.substring(1)
  }

  return cleaned;
}

class PhoneNumber {

  constructor(num, listOfRules = [clear, hasAlphaChars, hasIncorrectLength]){
    this.listOfRules = listOfRules;

    this.num = num;
  }

  //do not remove
  number() {
    return this.validate();
  }



  validate() {
    let obj = this.listOfRules.reduce((prev, next) => {
      const { original, cleaned } = prev;
      const newCleaned = next(original, cleaned);

      return { original, cleaned: newCleaned }
    }, { original: this.num });

    return obj.cleaned;
  }
}

export default PhoneNumber;

phone-number.spec.js

import PhoneNumber from './phone-number';

describe('PhoneNumber()', () => {
  test('cleans the number', () => {
    const phone = new PhoneNumber('(123) 456-7890');
    expect(phone.number()).toEqual('1234567890');
  });

  test('cleans numbers with dots', () => {
    const phone = new PhoneNumber('123.456.7890');
    expect(phone.number()).toEqual('1234567890');
  });

  test('cleans numbers with multiple spaces', () => {
    const phone = new PhoneNumber('123 456   7890   ');
    expect(phone.number()).toEqual('1234567890');
  });

  test('invalid when 9 digits', () => {
    const phone = new PhoneNumber('123456789');
    expect(phone.number()).toEqual(null);
  });

  test('invalid when 11 digits', () => {
    const phone = new PhoneNumber('21234567890');
    expect(phone.number()).toEqual(null);
  });

  test('valid when 11 digits and starting with 1', () => {
    const phone = new PhoneNumber('11234567890');
    expect(phone.number()).toEqual('1234567890');
  });

  test('invalid when 12 digits', () => {
    const phone = new PhoneNumber('321234567890');
    expect(phone.number()).toEqual(null);
  });

  test('invalid with letters', () => {
    const phone = new PhoneNumber('123-abc-7890');
    expect(phone.number()).toEqual(null);
  });

  test('invalid with punctuations', () => {
    const phone = new PhoneNumber('123-@:!-7890');
    expect(phone.number()).toEqual(null);
  });

  test('invalid with right number of digits but letters mixed in', () => {
    const phone = new PhoneNumber('1a2b3c4d5e6f7g8h9i0j');
    expect(phone.number()).toEqual(null);
  });
});