Are you aiming to strengthen your JavaScript logic skills? Whether you’re preparing for technical interviews, tackling coding assessments, or simply seeking to refine your problem-solving abilities, engaging with logic-building exercises is vital. In this collection, you’ll find 50 thoughtfully curated JavaScript logic questions, each accompanied by thorough explanations. These questions are designed to help you develop both fundamental and advanced understanding of JavaScript concepts. Dive in, challenge yourself, and deepen your mastery of JavaScript logic.
Introduction
JavaScript stands as a foundational language in modern web development. Mastery of logical structures is essential for producing efficient and reliable code. The following set of questions addresses a range of fundamental topics, including arrays, strings, loops, functions, and objects. Each question is accompanied by a succinct answer, designed to deepen your understanding of core concepts and enhance your programming proficiency.
50 JavaScript Logic Building Questions with Answers
Reverse a string in JavaScript.
function reverseString(str) {
return str.split('').reverse().join('');
}
// Example: reverseString("hello") => "olleh"Check if a string is a palindrome.
function isPalindrome(str) {
return str === str.split('').reverse().join('');
}
// Example: isPalindrome("madam") => trueFind the largest number in an array.
function largestNumber(arr) {
return Math.max(...arr);
}
// Example: largestNumber([1, 2, 3]) => 3Find the factorial of a number.
function factorial(n) {
return n === 0 ? 1 : n * factorial(n - 1);
}
// Example: factorial(5) => 120Check if a number is prime.
function isPrime(num) {
if (num < 2) return false;
for (let i = 2; i <= Math.sqrt(num); i++) {
if (num % i === 0) return false;
}
return true;
}
// Example: isPrime(7) => trueFind the sum of all numbers in an array.
function sumArray(arr) {
return arr.reduce((a, b) => a + b, 0);
}
// Example: sumArray([1,2,3]) => 6Remove duplicates from an array.
function removeDuplicates(arr) {
return [...new Set(arr)];
}
// Example: removeDuplicates([1,2,2,3]) => [1,2,3]Find the Fibonacci sequence up to n terms.
function fibonacci(n) {
let seq = [0, 1];
for (let i = 2; i < n; i++) {
seq.push(seq[i-1] + seq[i-2]);
}
return seq.slice(0, n);
}
// Example: fibonacci(5) => [0,1,1,2,3]Check if two strings are anagrams.
function areAnagrams(str1, str2) {
return str1.split('').sort().join('') === str2.split('').sort().join('');
}
// Example: areAnagrams("listen", "silent") => trueFind the second largest number in an array.
function secondLargest(arr) {
let unique = [...new Set(arr)];
unique.sort((a, b) => b - a);
return unique[1];
}
// Example: secondLargest([1,2,3,2]) => 2Count vowels in a string.
function countVowels(str) {
return (str.match(/[aeiou]/gi) || []).length;
}
// Example: countVowels("hello") => 2Find the missing number in an array of 1 to n.
function findMissing(arr, n) {
let total = (n * (n + 1)) / 2;
let sum = arr.reduce((a, b) => a + b, 0);
return total - sum;
}
// Example: findMissing([1,2,4,5], 5) => 3Capitalize the first letter of each word in a string.
function capitalizeWords(str) {
return str.replace(/\b\w/g, c => c.toUpperCase());
}
// Example: capitalizeWords("hello world") => "Hello World"Find the GCD of two numbers.
function gcd(a, b) {
return b === 0 ? a : gcd(b, a % b);
}
// Example: gcd(12, 8) => 4Find the LCM of two numbers.
function lcm(a, b) {
return (a * b) / gcd(a, b);
}
// Example: lcm(12, 8) => 24Check if a number is even or odd.
function isEven(num) {
return num % 2 === 0;
}
// Example: isEven(4) => trueFind the longest word in a string.
function longestWord(str) {
return str.split(' ').reduce((a, b) => a.length > b.length ? a : b);
}
// Example: longestWord("I love JavaScript") => "JavaScript"Count the number of words in a string.
function wordCount(str) {
return str.trim().split(/\s+/).length;
}
// Example: wordCount("Hello world!") => 2Check if an array is sorted.
function isSorted(arr) {
for (let i = 1; i < arr.length; i++) {
if (arr[i] < arr[i-1]) return false;
}
return true;
}
// Example: isSorted([1,2,3]) => trueFind the intersection of two arrays.
function intersection(arr1, arr2) {
return arr1.filter(x => arr2.includes(x));
}
// Example: intersection([1,2,3], [2,3,4]) => [2,3]Find the union of two arrays.
function union(arr1, arr2) {
return [...new Set([...arr1, ...arr2])];
}
// Example: union([1,2], [2,3]) => [1,2,3]Find the average of numbers in an array.
function average(arr) {
return arr.reduce((a, b) => a + b, 0) / arr.length;
}
// Example: average([1,2,3]) => 2Find all prime numbers up to n.
function primesUpTo(n) {
let primes = [];
for (let i = 2; i <= n; i++) {
if (isPrime(i)) primes.push(i);
}
return primes;
}
// Example: primesUpTo(10) => [2,3,5,7]Flatten a nested array.
function flatten(arr) {
return arr.flat(Infinity);
}
// Example: flatten([1, [2, [3]]]) => [1,2,3]Find the frequency of each element in an array.
function frequency(arr) {
return arr.reduce((acc, val) => {
acc[val] = (acc[val] || 0) + 1;
return acc;
}, {});
}
// Example: frequency([1,2,2,3]) => {1:1, 2:2, 3:1}Remove falsy values from an array.
function removeFalsy(arr) {
return arr.filter(Boolean);
}
// Example: removeFalsy([0,1,false,2,'',3]) => [1,2,3]Convert Celsius to Fahrenheit.
function cToF(c) {
return (c * 9/5) + 32;
}
// Example: cToF(0) => 32Convert Fahrenheit to Celsius.
function fToC(f) {
return (f - 32) * 5/9;
}
// Example: fToC(32) => 0Find the sum of digits of a number.
function sumDigits(num) {
return num.toString().split('').reduce((a, b) => a + Number(b), 0);
}
// Example: sumDigits(123) => 6Check if a year is a leap year.
function isLeapYear(year) {
return (year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0);
}
// Example: isLeapYear(2024) => trueFind the median of an array.
function median(arr) {
arr.sort((a, b) => a - b);
let mid = Math.floor(arr.length / 2);
return arr.length % 2 !== 0 ? arr[mid] : (arr[mid-1] + arr[mid]) / 2;
}
// Example: median([1,2,3]) => 2Find the mode of an array.
function mode(arr) {
let freq = frequency(arr);
let max = Math.max(...Object.values(freq));
return Object.keys(freq).filter(k => freq[k] === max);
}
// Example: mode([1,2,2,3]) => ["2"]Check if a string contains only digits.
function isDigits(str) {
return /^\d+$/.test(str);
}
// Example: isDigits("12345") => trueFind the first non-repeated character in a string.
function firstNonRepeated(str) {
for (let char of str) {
if (str.indexOf(char) === str.lastIndexOf(char)) return char;
}
return null;
}
// Example: firstNonRepeated("aabbcde") => "c"Check if an object is empty.
function isEmpty(obj) {
return Object.keys(obj).length === 0;
}
// Example: isEmpty({}) => trueClone an object.
function clone(obj) {
return {...obj};
}
// Example: clone({a:1}) => {a:1}Merge two objects.
function merge(obj1, obj2) {
return {...obj1, ...obj2};
}
// Example: merge({a:1}, {b:2}) => {a:1, b:2}Check if a string starts with a given substring.
function startsWith(str, sub) {
return str.startsWith(sub);
}
// Example: startsWith("hello", "he") => trueCheck if a string ends with a given substring.
function endsWith(str, sub) {
return str.endsWith(sub);
}
// Example: endsWith("hello", "lo") => trueRepeat a string n times.
function repeatString(str, n) {
return str.repeat(n);
}
// Example: repeatString("abc", 3) => "abcabcabc"Truncate a string to a specified length.
function truncate(str, len) {
return str.length > len ? str.slice(0, len) + "..." : str;
}
// Example: truncate("Hello World", 5) => "Hello..."Find all occurrences of a substring in a string.
function findAllOccurrences(str, sub) {
let indices = [];
let idx = str.indexOf(sub);
while (idx !== -1) {
indices.push(idx);
idx = str.indexOf(sub, idx + 1);
}
return indices;
}Convert a string to snake_case.
function toSnakeCase(str) {
return str.replace(/[A-Z]/g, c => '_' + c.toLowerCase()).replace(/\s+/g, '_');
}
// Example: toSnakeCase("helloWorld") => "hello_world"Check if a string is a valid email.
function isValidEmail(str) {
return /^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$/.test(str);
}
// Example: isValidEmail("test@example.com") => trueGenerate a random number between min and max.
function randomNumber(min, max) {
return Math.floor(Math.random() * (max - min + 1)) + min;
}
// Example: randomNumber(1, 10) => e.g., 7Check if two arrays are equal.
function arraysEqual(arr1, arr2) {
if (arr1.length !== arr2.length) return false;
return arr1.every((val, i) => val === arr2[i]);
}
// Example: arraysEqual([1,2,3], [1,2,3]) => trueRotate an array by k positions.
function rotateArray(arr, k) {
k %= arr.length;
return [...arr.slice(k), ...arr.slice(0, k)];
}
// Example: rotateArray([1,2,3,4], 2) => [3,4,1,2]Find the maximum product of two numbers in an array.
function maxProduct(arr) {
arr.sort((a, b) => b - a);
return arr[0] * arr[1];
}
// Example: maxProduct([1,5,3,2]) => 15Replace all occurrences of a character in a string.
function replaceChar(str, oldChar, newChar) {
return str.replace(RegExp(oldChar, 'g'), newChar);
}
// Example: replaceChar("hello", "l", "x") => "hexxo"Generate all permutations of a string.
function permute(str) {
if (str.length <= 1) return [str];
let result = [];
for (let i = 0; i < str.length; i++) {
let char = str[i];
let rest = str.slice(0, i) + str.slice(i + 1);
permute(rest).forEach(p => result.push(char + p));
}
return result;
}
// Example: permute("abc") => ["abc", "acb", "bac", "bca", "cab", "cba"]Conclusion
So, you’ve got 50 JavaScript brain teasers here—everything from the classic string shuffling and array wizardry to the wild stuff like permutations and making sneaky copies of objects. Honestly, grinding through these isn’t just about flexing for an interview (although, hey, it helps). It’s about actually getting sharper at picking apart problems and, you know, not panicking when that whiteboard marker squeaks. Just keep at it, mess around with more challenges, and before you know it, you’ll be the go-to JavaScript whiz everyone pesters for help. Happy coding—or, well, as happy as debugging lets you be!
