This list showcases some of the most popular JavaScript algorithms, from simple string manipulations to classic recursive solutions and efficient searching techniques. Each snippet demonstrates a fundamental concept often encountered in coding interviews and real-world development.
Note: Popularity is based on common interview topics, educational resources, and usage in developer communities.
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: true
Explanation : Determines if a string reads the same backward as forward using string reversal.
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: 3
Explanation : Searches for a target in a sorted array using a divide-and-conquer approach (Time complexity: O(log n)).
4. Fibonacci Sequence (Recursive) function fibonacci ( n ) {
if ( n <= 1 ) return n ;
return fibonacci ( n - 1 ) + fibonacci ( n - 2 ) ;
}
console . log ( fibonacci ( 6 ) ) ; // Output: 8
Explanation : Generates the nth Fibonacci number recursively by summing the two preceding numbers.
⚠️ Note : This approach has exponential time complexity O(2^n) and is inefficient for large inputs. Use memoization or iteration for better performance.
function factorial ( n ) {
if ( n === 0 ) return 1 ;
return n * factorial ( n - 1 ) ;
}
console . log ( factorial ( 5 ) ) ; // Output: 120
Explanation : Calculates the factorial of a number recursively by multiplying it with decremented values.
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: true
Explanation : Checks if a number is prime by testing divisibility up to its square root.
function findMax ( arr ) {
return Math . max ( ...arr ) ;
}
console . log ( findMax ( [ 1 , 2 , 3 , 4 , 5 ] ) ) ; // Output: 5
Explanation : Finds the largest number in an array using the Math.max function and the spread operator.
8. Merge Two Sorted Arrays 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 ] ) ;
i ++ ;
} else {
merged . push ( arr2 [ j ] ) ;
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 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 (Time complexity: O(n²)).
10. Find the GCD (Greatest Common Divisor) function gcd ( a , b ) {
if ( b === 0 ) return a ;
return gcd ( b , a % b ) ;
}
console . log ( gcd ( 48 , 18 ) ) ; // Output: 6
Explanation : Uses the Euclidean algorithm to compute the greatest common divisor of two numbers (Time complexity: O(log min(a, b))).
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