JavaScript Coding Challenges for beginners

Mastering these coding challenges may not get you a job at google... but you'll be one step closer to building your own JavaScript game at codeguppy.com.

These coding challenges are intended for beginners, therefore the solutions are implemented using only simple / classical programming elements. Each solution is acompanied by an online link that helps you quickly run it in a code playground at codeguppy.com

Note: The code is making use of the codeguppy specific function println() to print the results. If you want to run these solutions outside codeguppy.com, just replace println() with console.log() then run them using your browser console tool or node.js.

Coding challenge #1: Print numbers from 1 to 10

https://codeguppy.com/code.html?mrgCtLGA90Ozr0Otrs5Z

for(var i = 1; i <= 10; i++)
{
    println(i);
}

Coding challenge #2: Print the odd numbers less than 100

https://codeguppy.com/code.html?eDLA5XPp3bPxP79H2jKT

for(var i = 1; i <= 100; i += 2)
{
    println(i);
}

Coding challenge #3: Print the multiplication table with 7

https://codeguppy.com/code.html?fpnQzIhnGUUmCUZy1fyQ

for(var i = 1; i <= 10; i++)
{
    var row = "7 * " + i + " = " + 7 * i;
    println(row);
}

Coding challenge #4: Print all the multiplication tables with numbers from 1 to 10

https://codeguppy.com/code.html?78aD4mWSCzoNEVxOQ8tI

for(var i = 1; i <= 10; i++)
{
    printTable(i);
    println("");
}

function printTable(n)
{
    for(var i = 1; i <= 10; i++)
    {
        var row = n + " * " + i + " = " + n * i;
        println(row);
    }
}

Coding challenge #5: Calculate the sum of numbers from 1 to 10

https://codeguppy.com/code.html?Vy6u9kki2hXM4YjsbpuN

var sum = 0;

for(var i = 1; i <= 10; i++)
{
    sum += i;
}

println(sum);

Coding challenge #6: Calculate 10!

https://codeguppy.com/code.html?IIuJX4gnXOndNu0VrywA

var prod = 1;

for(var i = 1; i <= 10; i++)
{
    prod *= i;
}

println(prod);

Coding challenge #7: Calculate the sum of odd numbers greater than 10 and less than 30

https://codeguppy.com/code.html?DcOffOyoIArmNZHVNM2u

var sum = 0;

for(var i = 11; i <= 30; i += 2)
{
    sum += i;
}

println(sum);

Coding challenge #8: Create a function that will convert from Celsius to Fahrenheit

https://codeguppy.com/code.html?oI5mWm6QIMRjY1m9XAmI

function celsiusToFahrenheit(n)
{
    return n * 1.8 + 32;
}

var r = celsiusToFahrenheit(20);
println(r);

Coding challenge #9: Create a function that will convert from Fahrenheit to Celsius

https://codeguppy.com/code.html?mhnf8DpPRqqgsBgbJNpz

function fahrenheitToCelsius(n)
{
    return (n - 32) / 1.8;
}

var r = fahrenheitToCelsius(68);
println(r);

Coding challenge #10: Calculate the sum of numbers in an array of numbers

https://codeguppy.com/code.html?TteeVr0aj33ZyCLR685L

function sumArray(ar)
{
    var sum = 0;
    
    for(var i = 0; i < ar.length; i++)
    {
        sum += ar[i];
    }
    
    return sum;
}

var ar = [2, 3, -1, 5, 7, 9, 10, 15, 95];
var sum = sumArray(ar);
println(sum);

Coding challenge #11: Calculate the average of the numbers in an array of numbers

https://codeguppy.com/code.html?7i9sje6FuJsI44cuncLh

function averageArray(ar)
{
    var n = ar.length;
    var sum = 0;
    
    for(var i = 0; i < n; i++)
    {
        sum += ar[i];
    }
    
    return sum / n;
}

var ar = [1, 3, 9, 15, 90];
var avg = averageArray(ar);

println("Average: ", avg);

Coding challenge #12: Create a function that receives an array of numbers and returns an array containing only the positive numbers

Solution 1:

https://codeguppy.com/code.html?0eztj1v6g7iQLzst3Id3

function getPositives(ar)
{
    var ar2 = [];
    
    for(var i = 0; i < ar.length; i++)
    {
        var el = ar[i];
        
        if (el >= 0)
        {
            ar2.push(el);
        }
    }
    
    return ar2;
}

var ar = [-5, 10, -3, 12, -9, 5, 90, 0, 1];
var ar2 = getPositives(ar);

println(ar2);

Coding challenge #12: Create a function that receives an array of numbers and returns an array containing only the positive numbers

Solution 2

https://codeguppy.com/code.html?KefrPtrvJeMpQyrB8V2D

function getPositives(ar)
{
    var ar2 = [];
    
    for(var el of ar)
    {
        if (el >= 0)
        {
            ar2.push(el);
        }
    }
    
    return ar2;
}

var ar = [-5, 10, -3, 12, -9, 5, 90, 0, 1];
var ar2 = getPositives(ar);

println(ar2);

Coding challenge #12: Create a function that receives an array of numbers and returns an array containing only the positive numbers

Solution 3

https://codeguppy.com/code.html?qJBQubNA7z10n6pjYmB8

function getPositives(ar)
{
    return ar.filter(el => el >= 0);
}

var ar = [-5, 10, -3, 12, -9, 5, 90, 0, 1];
var ar2 = getPositives(ar);
println(ar2);

Coding challenge #13: Find the maximum number in an array of numbers

https://codeguppy.com/code.html?THmQGgOMRUj6PSvEV8HD

function findMax(ar)
{
    var max = ar[0];
    
    for(var i = 0; i < ar.length; i++)
    {
        if (ar[i] > max)
        {
            max = ar[i];
        }
    }
    
    return max;
}

var ar = [-5, 10, -3, 12, -9, 5, 90, 0, 1];
var max = findMax(ar);
println("Max: ", max);

Coding challenge #14: Print the first 10 Fibonacci numbers without recursion

https://codeguppy.com/code.html?rKOfPxHbVwxNWI2d8orH

var f0 = 0;
println(f0);

var f1 = 1;
println(f1);

for(var i = 2; i < 10; i++)
{
    var fi = f1 + f0;
    println(fi);
    
    f0 = f1;
    f1 = fi;
}

Coding challenge #15: Create a function that will find the nth Fibonacci number using recursion

https://codeguppy.com/code.html?IneuIg9O0rRV8V76omBk

function findFibonacci(n)
{
    if (n == 0)
        return 0;
        
    if (n == 1)
        return 1;
        
    return findFibonacci(n - 1) + findFibonacci(n - 2);
}

var n = findFibonacci(10);
println(n);

Coding challenge #16: Create a function that will return a Boolean specifying if a number is prime

https://codeguppy.com/code.html?fRYsPEc2vcZTbIU8MKku

function isPrime(n)
{
    if (n < 2)
        return false;
        
    if (n == 2)
        return true;
    
    var maxDiv = Math.sqrt(n);
    
    for(var i = 2; i <= maxDiv; i++)
    {
        if (n % i == 0)
        {
            return false;
        }
    }
    
    return true;
}

println(2, " is prime? ", isPrime(2));
println(3, " is prime? ", isPrime(3));
println(4, " is prime? ", isPrime(4));
println(5, " is prime? ", isPrime(5));
println(9, " is prime? ", isPrime(9));

Coding challenge #17: Calculate the sum of digits of a positive integer number

https://codeguppy.com/code.html?RHA714FYio8gWgmjWYPz

function sumDigits(n)
{
    var s = n.toString();
    var sum = 0;
    
    for(var char of s)
    {
        var digit = parseInt(char);
        sum += digit;
    }
    
    return sum;
}

var sum = sumDigits(1235231);
println("Sum: ", sum);

Coding challenge #18: Print the first 100 prime numbers

https://codeguppy.com/code.html?gnMVeOZXN6VhLekyvui8

printPrimes(100);

// Function prints the first nPrimes numbers
function printPrimes(nPrimes)
{
    var n = 0;
    var i = 2;
    
    while(n < nPrimes)
    {
        if (isPrime(i))
        {
            println(n, " --> ", i);
            n++;
        }
        
        i++;
    }
}


// Returns true if a number is prime
function isPrime(n)
{
    if (n < 2)
        return false;
        
    if (n == 2)
        return true;
    
    var maxDiv = Math.sqrt(n);
    
    for(var i = 2; i <= maxDiv; i++)
    {
        if (n % i == 0)
        {
            return false;
        }
    }
    
    return true;
}

Coding challenge #19: Create a function that will return in an array the first "nPrimes" prime numbers greater than a particular number "startAt"

https://codeguppy.com/code.html?mTi7EdKrviwIn4bfrmM7

println(getPrimes(10, 100));

function getPrimes(nPrimes, startAt)
{
    var ar = [];
    
    var i = startAt;
    
    while(ar.length < nPrimes)
    {
        if (isPrime(i))
        {
            ar.push(i);
        }
        
        i++;
    }
    
    return ar;
}

// Returns true if a number is prime
function isPrime(n)
{
    if (n < 2)
        return false;
        
    if (n == 2)
        return true;
    
    var maxDiv = Math.sqrt(n);
    
    for(var i = 2; i <= maxDiv; i++)
    {
        if (n % i == 0)
        {
            return false;
        }
    }
    
    return true;
}

Coding challenge #20: Rotate an array to the left 1 position

https://codeguppy.com/code.html?MRmfvuQdZpHn0k03hITn

var ar = [1, 2, 3];
rotateLeft(ar);
println(ar);

function rotateLeft(ar)
{
    var first = ar.shift();
    ar.push(first);
}

Coding challenge #21: Rotate an array to the right 1 position

https://codeguppy.com/code.html?fHfZqUmkAVUXKtRupmzZ

var ar = [1, 2, 3];
rotateRight(ar);
println(ar);

function rotateRight(ar)
{
    var last = ar.pop();
    ar.unshift(last);
}

Coding challenge #22: Reverse an array

https://codeguppy.com/code.html?GZddBqBVFlqYrsxi3Vbu

var ar = [1, 2, 3];
var ar2 = reverseArray(ar);
println(ar2);

function reverseArray(ar)
{
    var ar2 = [];
    
    for(var i = ar.length - 1; i >= 0; i--)
    {
        ar2.push(ar[i]);
    }
    
    return ar2;
}

Coding challenge #23: Reverse a string

https://codeguppy.com/code.html?pGpyBz0dWlsj7KR3WnFF

var s = reverseString("JavaScript");
println(s);

function reverseString(s)
{
    var s2 = "";
    
    for(var i = s.length - 1; i >= 0; i--)
    {
        var char = s[i];
        s2 += char;
    }
    
    return s2;
}

Coding challenge #24: Create a function that will merge two arrays and return the result as a new array