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📚 A list of popular JavaScript algorithms that you'll encounter in the real world. 🧠
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AllThingsSmitty/javascript-algorithms
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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)
functionreverseString(str){returnstr.split("").reverse().join("");}console.log(reverseString("hello"));// Output: "olleh"
Explanation: Reverses the characters in a string by splitting, reversing, and joining them back together.
functionisPalindrome(str){returnstr===str.split("").reverse().join("");}console.log(isPalindrome("racecar"));// Output: true
Explanation: Determines if a string reads the same backward as forward using string reversal.
functioncharFrequency(str){constfreq={};for(letcharofstr){freq[char]=(freq[char]||0)+1;}returnfreq;}console.log(charFrequency("hello"));// Output: { h: 1, e: 1, l: 2, o: 1 }
Explanation: Counts how often each character appears in a string.
functionisAnagram(str1,str2){constnormalize=(str)=>str.split("").sort().join("");returnnormalize(str1)===normalize(str2);}console.log(isAnagram("listen","silent"));// Output: true
Explanation: Determines if two strings are anagrams by sorting and comparing them.
functionisPrime(num){if(num<=1)returnfalse;for(leti=2;i<=Math.sqrt(num);i++){if(num%i===0)returnfalse;}returntrue;}console.log(isPrime(7));// Output: true
Explanation: Checks if a number is prime by testing divisibility up to its square root.
functionfibonacci(n){if(n<=1)returnn;returnfibonacci(n-1)+fibonacci(n-2);}console.log(fibonacci(6));// Output: 8
Explanation: Generates the nth Fibonacci number recursively by summing the two preceding numbers.
O(2^n) and is inefficient for large inputs.
functionfactorial(n){if(n<0)thrownewRangeError("Factorial is not defined for negative numbers");if(n===0||n===1)return1;returnn*factorial(n-1);}console.log(factorial(5));// Output: 120
Explanation: Calculates the factorial of a number recursively by multiplying it with decremented values.
functiongcd(a,b){if(b===0)returna;returngcd(b,a%b);}console.log(gcd(48,18));// Output: 6
Explanation: Uses the Euclidean algorithm to compute the greatest common divisor.
functiontwoSum(nums,target){constmap=newMap();for(leti=0;i<nums.length;i++){constcomplement=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.
functionbinarySearch(arr,target){letleft=0,right=arr.length-1;while(left<=right){constmid=Math.floor((left+right)/2);if(arr[mid]===target)returnmid;if(arr[mid]<target)left=mid+1;elseright=mid-1;}return-1;}console.log(binarySearch([1,2,3,4,5],4));// Output: 3
Explanation: Searches for a target in a sorted array using a divide-and-conquer approach.
functionbubbleSort(arr){for(leti=0;i<arr.length;i++){for(letj=0;j<arr.length-i-1;j++){if(arr[j]>arr[j+1]){[arr[j],arr[j+1]]=[arr[j+1],arr[j]];}}}returnarr;}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.
functionquickSort(arr){if(arr.length<=1)returnarr;constpivot=arr[arr.length-1];constleft=[],right=[];for(leti=0;i<arr.length-1;i++){if(arr[i]<pivot)left.push(arr[i]);elseright.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 ofO(n log n).
functionmergeSortedArrays(arr1,arr2){letmerged=[],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++]);}}returnmerged.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.
functionfindMax(arr){returnMath.max(...arr);}console.log(findMax([1,2,3,4,5]));// Output: 5
Explanation: Finds the largest number in an array using theMath.max function and spread operator.
functiondebounce(fn,delay){lettimer;returnfunction(...args){clearTimeout(timer);timer=setTimeout(()=>fn.apply(this,args),delay);};}constlog=debounce(()=>console.log("Debounced!"),300);log();log();log();// Logs once after 300ms of inactivity
Explanation: Limits the rate at which a function can fire, commonly used in event handling (e.g., input, scroll).
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