JavaScript: Letter combinations of a number

JavaScript Function: Exercise-13 with Solution

A string consists of digits ranging from 2 to 9, inclusive.
Write a JavaScript program to get all possible letter combinations that can represent the number using recursion.

Letter Combination:
1: 'abc',
2: 'def',
3: 'ghi',
4: 'jkl',
5: 'mno',
6: 'pqr',
7: 'stu',
8: 'vwx'
9: 'yz'

Test Data:
("12") -> ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]
("9") -> ["y", "z"]

Sample Solution:

HTML Code:

<!DOCTYPE html>
  <meta charset="utf-8">
  <title>Letter combinations of a number</title>


JavaScript Code:

const test = (digits) => {
  const length = digits?.length
  const result = []
  if (!length) {
    return result
  const digit_Map = {
    1: 'abc',
    2: 'def',
    3: 'ghi',
    4: 'jkl',
    5: 'mno',
    6: 'pqr',
    7: 'stu',
    8: 'vwx',
    9: 'yz'

  const letter_combinations = (index, combination) => {
    let letter
    let letterIndex
    if (index >= length) {
    const digit = digit_Map[digits[index]]
    letterIndex = 0
    while ((letter = digit[letterIndex++])) {
      letter_combinations(index + 1, combination + letter)
  letter_combinations(0, '')
  return result




Flowchart: JavaScript recursion function- Letter combinations of a number.

Live Demo:

See the Pen javascript-recursion-function-exercise-13 by w3resource (@w3resource) on CodePen.

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Previous: Binary Search Algorithm using recursion.
Next:Javascript Conditional Statements and Loops Exercises

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JavaScript: Tips of the Day

function and arguments

const person = {
  name: 'Lydia Hallie',
  hobbies: ['coding'],

function addHobby(hobby, hobbies = person.hobbies) {
  return hobbies;

addHobby('running', []);
addHobby('baking', person.hobbies);


The addHobby function receives two arguments, hobby and hobbies with the default value of the hobbies array on the person object.
First, we invoke the addHobby function, and pass "running" as the value for hobby and an empty array as the value for hobbies. Since we pass an empty array as the value for y, "running" gets added to this empty array.
Then, we invoke the addHobby function, and pass "dancing" as the value for hobby. We didn't pass a value for hobbies, so it gets the default value, the hobbies property on the person object. We push the hobby dancing to the person.hobbies array.
Last, we invoke the addHobby function, and pass "bdaking" as the value for hobby, and the person.hobbies array as the value for hobbies. We push the hobby baking to the person.hobbies array.
After pushing dancing and baking, the value of person.hobbies is ["coding", "dancing", "baking"]

Ref: https://bit.ly/2Hcpkm6