This repository contains a curated list of JavaScript algorithms, organized by category. These range from simple string manipulation to advanced searching and sorting techniques — perfect for interviews and foundational learning.
Note
Popularity is based on common interview topics, educational materials, and developer community usage.
- Prime Number Check
- Fibonacci Sequence (Recursive)
- Factorial of a Number
- Find the GCD (Greatest Common Divisor)
function reverseString(str) {
return str.split("").reverse().join("");
}
console.log(reverseString("hello")); // Output: "olleh"Explanation: Reverses the characters in a string by splitting, reversing, and joining them back together.
function isPalindrome(str) {
return str === str.split("").reverse().join("");
}
console.log(isPalindrome("racecar")); // Output: trueExplanation: Determines if a string reads the same backward as forward using string reversal.
function charFrequency(str) {
const freq = {};
for (let char of str) {
freq[char] = (freq[char] || 0) + 1;
}
return freq;
}
console.log(charFrequency("hello")); // Output: { h: 1, e: 1, l: 2, o: 1 }Explanation: Counts how often each character appears in a string.
function isAnagram(str1, str2) {
const normalize = (str) => str.split("").sort().join("");
return normalize(str1) === normalize(str2);
}
console.log(isAnagram("listen", "silent")); // Output: trueExplanation: Determines if two strings are anagrams by sorting and comparing them.
function isPrime(num) {
if (num <= 1) return false;
for (let i = 2; i <= Math.sqrt(num); i++) {
if (num % i === 0) return false;
}
return true;
}
console.log(isPrime(7)); // Output: trueExplanation: Checks if a number is prime by testing divisibility up to its square root.
function fibonacci(n) {
if (n <= 1) return n;
return fibonacci(n - 1) + fibonacci(n - 2);
}
console.log(fibonacci(6)); // Output: 8Explanation: Generates the nth Fibonacci number recursively by summing the two preceding numbers.
O(2^n) and is inefficient for large inputs.
function factorial(n) {
if (n < 0)
throw new RangeError("Factorial is not defined for negative numbers");
if (n === 0 || n === 1) return 1;
return n * factorial(n - 1);
}
console.log(factorial(5)); // Output: 120Explanation: Calculates the factorial of a number recursively by multiplying it with decremented values.
function gcd(a, b) {
if (b === 0) return a;
return gcd(b, a % b);
}
console.log(gcd(48, 18)); // Output: 6Explanation: Uses the Euclidean algorithm to compute the greatest common divisor.
function twoSum(nums, target) {
const map = new Map();
for (let i = 0; i < nums.length; i++) {
const complement = target - nums[i];
if (map.has(complement)) return [map.get(complement), i];
map.set(nums[i], i);
}
return [];
}
console.log(twoSum([2, 7, 11, 15], 9)); // Output: [0, 1]Explanation: Finds two indices such that their values sum to the target using a hash map.
function binarySearch(arr, target) {
let left = 0,
right = arr.length - 1;
while (left <= right) {
const mid = Math.floor((left + right) / 2);
if (arr[mid] === target) return mid;
if (arr[mid] < target) left = mid + 1;
else right = mid - 1;
}
return -1;
}
console.log(binarySearch([1, 2, 3, 4, 5], 4)); // Output: 3Explanation: Searches for a target in a sorted array using a divide-and-conquer approach.
function bubbleSort(arr) {
for (let i = 0; i < arr.length; i++) {
for (let j = 0; j < arr.length - i - 1; j++) {
if (arr[j] > arr[j + 1]) {
[arr[j], arr[j + 1]] = [arr[j + 1], arr[j]];
}
}
}
return arr;
}
console.log(bubbleSort([5, 3, 8, 4, 2])); // Output: [2, 3, 4, 5, 8]Explanation: Sorts an array by repeatedly swapping adjacent elements if they are in the wrong order.
function quickSort(arr) {
if (arr.length <= 1) return arr;
const pivot = arr[arr.length - 1];
const left = [],
right = [];
for (let i = 0; i < arr.length - 1; i++) {
if (arr[i] < pivot) left.push(arr[i]);
else right.push(arr[i]);
}
return [...quickSort(left), pivot, ...quickSort(right)];
}
console.log(quickSort([3, 6, 8, 10, 1, 2, 1])); // Output: [1, 1, 2, 3, 6, 8, 10]Explanation: A divide-and-conquer sorting algorithm with an average-case time complexity of O(n log n).
function mergeSortedArrays(arr1, arr2) {
let merged = [], i = 0, j = 0;
while (i < arr1.length && j < arr2.length) {
if (arr1[i] < arr2[j]) {
merged.push(arr1[i++]);
} else {
merged.push(arr2[j++]);
}
}
return merged.concat(arr1.slice(i)).concat(arr2.slice(j));
}
console.log(mergeSortedArrays([1, 3, 5], [2, 4, 6])); // Output: [1, 2, 3, 4, 5, 6]Explanation: Merges two sorted arrays into one sorted array by comparing elements sequentially.
function findMax(arr) {
return Math.max(...arr);
}
console.log(findMax([1, 2, 3, 4, 5])); // Output: 5Explanation: Finds the largest number in an array using the Math.max function and spread operator.
function debounce(fn, delay) {
let timer;
return function (...args) {
clearTimeout(timer);
timer = setTimeout(() => fn.apply(this, args), delay);
};
}
const log = debounce(() => console.log("Debounced!"), 300);
log();
log();
log(); // Logs once after 300ms of inactivityExplanation: Limits the rate at which a function can fire, commonly used in event handling (e.g., input, scroll).