JavaScript: Data aggregation (Strings)

Aggregation applies not only to numbers but also to strings. These are tasks in which a string is built dynamically, that is, it is not known in advance how big it will be or what it will contain.

Imagine a function that can "multiply" a string, that is, it repeats it a specified number of times:

repeat('hexlet', 3); // hexlethexlethexlet

The way this function works is quite simple: in a loop, the string is "grown" the specified number of times:

const repeat = (text, times) => {
  // The neutral element for strings is the empty string
  let result = '';
  let i = 1;

  while (i <= times) {
    // Each time we add the string to the result
    result = `${result}${text}`;
    i = i + 1;
  }

  return result;
};

Let's break down the execution of this code step by step:

// For the call repeat('hexlet', 3);
let result = '';
result = `${result}hexlet`; // hexlet
result = `${result}hexlet`; // hexlethexlet
result = `${result}hexlet`; // hexlethexlethexlet

Visually, the process of growing the string looks like this:

repeat('hexlet', 3):

i=1: result = ''             + 'hexlet' = 'hexlet'
i=2: result = 'hexlet'       + 'hexlet' = 'hexlethexlet'
i=3: result = 'hexlethexlet' + 'hexlet' = 'hexlethexlethexlet'
                                            └── result

Neutral element

For growing to work, a starting value is needed. For strings, this value is the empty string ''.

It is called the neutral element because it changes nothing during concatenation:

console.log('' + 'abc'); // => abc
console.log('abc' + ''); // => abc

That is why the empty string is always used as the initial value when aggregating strings.

Instructions

Implement a function sanitizePhoneNumber() that takes a phone number from a form and returns a string without spaces, parentheses, and hyphens.

Users enter numbers in different ways, but before saving them they are normalized to a single format. Go through the original string character by character and assemble a new number using only the useful characters.

sanitizePhoneNumber('+7 (999) 123-45-67'); // => '+79991234567'
sanitizePhoneNumber('8 800 555 35 35');    // => '88005553535'
sanitizePhoneNumber('(123) 456-7890');     // => '1234567890'

Use the empty string as the initial value.

Коммерческий опыт и Трудоустройство

Tips

Iteration

The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.

In my environment the code works, but not here 🤨

My code is different from the teacher's one 🤔

I've read the lessons but nothing is clear 🙄

Прочитал урок — ничего не понятно 🙄

Found a bug? Have something to add? Pull requests are welcome!

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Your exercise will be checked with these tests:

import { expect, test } from 'vitest';
import f from './index.js';

test('test', () => {
  expect(f('+7 (999) 123-45-67')).toBe('+79991234567');
  expect(f('8 800 555 35 35')).toBe('88005553535');
  expect(f('(123) 456-7890')).toBe('1234567890');
});

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Teacher's solution will be available in:

20:00

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