readme.md

Challenge: Format Phone Number

Instructions

Write a function called formatPhoneNumber that takes in an array of numbers and returns a string representing the phone number formed by concatenating the numbers in the specified format.

Function Signature

/**
 * Returns a string representing a phone number.
 * @param {number[]} numbers - The numbers to use in the phone number.
 * @returns {string} - The formatted phone number.
 */
function formatPhoneNumber(numbers: number[]): string;

Examples

formatPhoneNumber([1, 2, 3, 4, 5, 6, 7, 8, 9, 0]); // => "(123) 456-7890"
formatPhoneNumber([5, 1, 9, 5, 5, 5, 4, 4, 6, 8]); // => "(519) 555-4468"
formatPhoneNumber([3, 4, 5, 5, 0, 1, 2, 5, 2, 7]); // => "(345) 501-2527"

Constraints

• The input array will always have 10 numbers
• The numbers can be any integer from 0 to 9

Hints

• You can use the Array.join method to concatenate the numbers in the array.
• You can use the Array.slice method to get a subset of the array.

Solutions

Click For Solution 1

function formatPhoneNumber(numbers) {
  const areaCode = numbers.slice(0, 3).join('');
  const prefix = numbers.slice(3, 6).join('');
  const lineNumber = numbers.slice(6).join('');

  return `(${areaCode}) ${prefix}-${lineNumber}`;
}

Explanation

• Create 3 variables to store the area code, prefix, and line number.
• Use the Array.slice method to get a subset of the array.
• Use the Array.join method to concatenate the numbers in the array.

Click For Solution 2

function formatPhoneNumber(numbers) {
  const formatted = numbers.join('');
  return `(${formatted.substring(0, 3)}) ${formatted.substring(
    3,
    6
  )}-${formatted.substring(6)}`;
}

Explanation

• Created a variable to store the numbers in the array concatenated together.
• Use the String.substring method to get a subset of the string.

Click For Solution 3

One line arrow function:

const formatPhoneNumber = (numbers) =>
  `(${numbers.slice(0, 3).join('')}) ${numbers.slice(3, 6).join('')}-${numbers
    .slice(6)
    .join('')}`;

Explanation

This is similar to the second solution, but we used an arrow function and Array.slice method chaining.

Test Cases

test('Format Phone Number', () => {
  expect(formatPhoneNumber([1, 2, 3, 4, 5, 6, 7, 8, 9, 0])).toBe(
    '(123) 456-7890'
  );
  expect(formatPhoneNumber([5, 0, 2, 4, 8, 1, 9, 6, 3, 7])).toBe(
    '(502) 481-9637'
  );
  expect(formatPhoneNumber([9, 9, 9, 9, 9, 9, 9, 9, 9, 9])).toBe(
    '(999) 999-9999'
  );
});