JavaScript Notes

JavaScript Beginner Practice Problems — 20+ Coding Exercises 2026

Master JavaScript fundamentals with 20+ beginner-level practice problems covering variables, loops, functions, strings, and arrays. Each problem includes solution code and expected output.

Welcome to the WoHoTech JavaScript Beginner Practice Set! This page contains 25 carefully crafted problems that cover all fundamental JavaScript concepts. Each problem includes a clear problem statement, a working solution, and the expected output.

Who Is This For?

Students learning JavaScript for the first time
Anyone preparing for junior developer interviews
Self-learners who want to solidify their fundamentals

Topics Covered

Variables & Data Types → Operators → Conditionals (if/else) → Loops (for, while) → Functions → Strings → Basic Arrays

Problem 2: Check Even or Odd

Problem: Write a function that checks whether a given number is even or odd.

js example

function checkEvenOdd(num) {
  if (num % 2 === 0) {
    return num + " is Even";
  } else {
    return num + " is Odd";
  }
}

console.log(checkEvenOdd(4));
console.log(checkEvenOdd(7));
console.log(checkEvenOdd(0));

Output

4 is Even
7 is Odd
0 is Even

Problem 3: Find the Largest of Three Numbers

Problem: Write a function that takes three numbers and returns the largest one.

js example

function findLargest(a, b, c) {
  if (a >= b && a >= c) {
    return a;
  } else if (b >= a && b >= c) {
    return b;
  } else {
    return c;
  }
}

console.log(findLargest(10, 25, 15));
console.log(findLargest(99, 45, 99));
console.log(findLargest(3, 7, 5));

Output

25
99
7

Problem 4: Celsius to Fahrenheit Conversion

Problem: Write a function to convert temperature from Celsius to Fahrenheit. Formula: F = (C × 9/5) + 32

js example

function celsiusToFahrenheit(celsius) {
  let fahrenheit = (celsius * 9/5) + 32;
  return celsius + "°C = " + fahrenheit + "°F";
}

console.log(celsiusToFahrenheit(0));
console.log(celsiusToFahrenheit(100));
console.log(celsiusToFahrenheit(37));

Output

0°C = 32°F
100°C = 212°F
37°C = 98.6°F

Problem 5: Calculate Factorial

Problem: Write a function to calculate the factorial of a number using a loop. Factorial of n = n × (n-1) × (n-2) × ... × 1

Example

function factorial(n) { if (n < 0) return "Undefined for negative numbers"; let result = 1; for (let i = 2; i <= n; i++) { result *= i; } return result; } console.log("5! =", factorial(5)); console.log("0! =", factorial(0)); console.log("8! =", factorial(8));

Output

5! = 120
0! = 1
8! = 40320

Problem 6: Multiplication Table

Problem: Write a program to print the multiplication table of a given number.

Example

function printTable(num) { for (let i = 1; i <= 10; i++) { console.log(num + " x " + i + " = " + (num * i)); } } printTable(7);

Output

7 x 1 = 7
7 x 2 = 14
7 x 3 = 21
7 x 4 = 28
7 x 5 = 35
7 x 6 = 42
7 x 7 = 49
7 x 8 = 56
7 x 9 = 63
7 x 10 = 70

Problem 7: Sum of Natural Numbers

Problem: Write a function to calculate the sum of first N natural numbers using a while loop.

Example

function sumOfNaturals(n) { let sum = 0; let i = 1; while (i <= n) { sum += i; i++; } return sum; } console.log("Sum of first 10:", sumOfNaturals(10)); console.log("Sum of first 50:", sumOfNaturals(50)); console.log("Sum of first 100:", sumOfNaturals(100));

Output

Sum of first 10: 55
Sum of first 50: 1275
Sum of first 100: 5050

Problem 8: Reverse a String

Problem: Write a function that reverses a string without using the built-in reverse() method.

Example

function reverseString(str) { let reversed = ""; for (let i = str.length - 1; i >= 0; i--) { reversed += str[i]; } return reversed; } console.log(reverseString("hello")); console.log(reverseString("JavaScript")); console.log(reverseString("WoHoTech"));

Output

olleh
tpircSavaJ
hceToHoW

Problem 9: Check Palindrome

Problem: Write a function that checks if a given string is a palindrome (reads the same forwards and backwards).

Example

function isPalindrome(str) { let cleaned = str.toLowerCase(); let reversed = ""; for (let i = cleaned.length - 1; i >= 0; i--) { reversed += cleaned[i]; } return cleaned === reversed; } console.log(isPalindrome("madam")); console.log(isPalindrome("racecar")); console.log(isPalindrome("hello")); console.log(isPalindrome("Level"));

Output

true
true
false
true

Problem 10: FizzBuzz

Problem: Print numbers from 1 to 20. For multiples of 3 print "Fizz", for multiples of 5 print "Buzz", for multiples of both print "FizzBuzz".

Example

Output

1
2
Fizz
4
Buzz
Fizz
7
8
Fizz
Buzz
11
Fizz
13
14
FizzBuzz

Problem 11: Count Vowels in a String

Problem: Write a function that counts the number of vowels in a given string.

Example

Output

hello: 2
JavaScript: 3
aEiOu: 5

Problem 12: Sum of Array Elements

Problem: Write a function that calculates the sum of all elements in an array.

Example

function sumArray(arr) { let sum = 0; for (let i = 0; i < arr.length; i++) { sum += arr[i]; } return sum; } console.log(sumArray([1, 2, 3, 4, 5])); console.log(sumArray([10, 20, 30])); console.log(sumArray([-5, 5, -10, 10]));

Output

15
60
0

Problem 13: Find the Largest Element in an Array

Problem: Write a function to find the largest element in an array without using Math.max().

Example

Output

9
200
-1

Problem 14: Fibonacci Series

Problem: Write a function to print the first N numbers of the Fibonacci series. Each number is the sum of the two preceding ones.

Example

function fibonacci(n) { let fib = [0, 1]; for (let i = 2; i < n; i++) { fib[i] = fib[i - 1] + fib[i - 2]; } return fib.join(", "); } console.log("First 8:", fibonacci(8)); console.log("First 10:", fibonacci(10));

Output

First 8: 0, 1, 1, 2, 3, 5, 8, 13
First 10: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34

Problem 15: Check Prime Number

Problem: Write a function that checks if a number is prime. A prime number is only divisible by 1 and itself.

js example

function isPrime(num) {
  if (num <= 1) return false;
  if (num <= 3) return true;
  if (num % 2 === 0) return false;

  for (let i = 3; i <= Math.sqrt(num); i += 2) {
    if (num % i === 0) return false;
  }
  return true;
}

console.log("2 is prime:", isPrime(2));
console.log("17 is prime:", isPrime(17));
console.log("25 is prime:", isPrime(25));
console.log("1 is prime:", isPrime(1));

Output

2 is prime: true
17 is prime: true
25 is prime: false
1 is prime: false

Problem 16: Count Digits in a Number

Problem: Write a function that counts how many digits are in a given number.

Example

function countDigits(num) { num = Math.abs(num); if (num === 0) return 1; let count = 0; while (num > 0) { num = Math.floor(num / 10); count++; } return count; } console.log("12345:", countDigits(12345)); console.log("100:", countDigits(100)); console.log("-9876:", countDigits(-9876)); console.log("0:", countDigits(0));

Output

Problem 17: Reverse an Array

Problem: Write a function to reverse an array without using the built-in reverse() method.

Example

function reverseArray(arr) { let reversed = []; for (let i = arr.length - 1; i >= 0; i--) { reversed.push(arr[i]); } return reversed; } console.log(reverseArray([1, 2, 3, 4, 5])); console.log(reverseArray(["a", "b", "c"])); console.log(reverseArray([true, false, true]));

Output

[ 5, 4, 3, 2, 1 ]
[ 'c', 'b', 'a' ]
[ true, false, true ]

Problem 18: Check Leap Year

Problem: Write a function to check whether a given year is a leap year. A year is leap if divisible by 4, except century years which must be divisible by 400.

js example

function isLeapYear(year) {
  if (year % 400 === 0) return true;
  if (year % 100 === 0) return false;
  if (year % 4 === 0) return true;
  return false;
}

console.log("2024:", isLeapYear(2024));
console.log("2026:", isLeapYear(2026));
console.log("2000:", isLeapYear(2000));
console.log("1900:", isLeapYear(1900));

Output

2024: true
2026: false
2000: true
1900: false

Problem 19: Find Second Largest in Array

Problem: Write a function to find the second largest number in an array.

Example

Output

40
8
90

Problem 20: Simple Calculator Using Functions

Problem: Write a calculator program that performs basic arithmetic operations using functions.

Example

function calculator(a, b, operator) { switch (operator) { case "+": return a + b; case "-": return a - b; case "*": return a * b; case "/": if (b === 0) return "Cannot divide by zero"; return a / b; default: return "Invalid operator"; } } console.log("10 + 5 =", calculator(10, 5, "+")); console.log("20 - 8 =", calculator(20, 8, "-")); console.log("6 * 7 =", calculator(6, 7, "*")); console.log("15 / 3 =", calculator(15, 3, "/")); console.log("10 / 0 =", calculator(10, 0, "/"));

Output

10 + 5 = 15
20 - 8 = 12
6 * 7 = 42
15 / 3 = 5
10 / 0 = Cannot divide by zero

Problem 21: Remove Duplicates from Array

Problem: Write a function to remove duplicate values from an array using basic loops.

Example

Output

[ 1, 2, 3, 4, 5 ]
[ 'a', 'b', 'c' ]
[ 10 ]

Problem 22: Generate a Simple Star Pattern

Problem: Write a program to print a right-angled triangle star pattern with N rows.

Example

function starPattern(rows) { for (let i = 1; i <= rows; i++) { let line = ""; for (let j = 1; j <= i; j++) { line += "* "; } console.log(line); } } starPattern(5);

Output

* 
* * 
* * * 
* * 
* * * 
* * * * 
* * * * *

Problem 23: Sum of Digits of a Number

Problem: Write a function that calculates the sum of all digits in a given number.

js example

function sumOfDigits(num) {
  num = Math.abs(num);
  let sum = 0;
  while (num > 0) {
    sum += num % 10;
    num = Math.floor(num / 10);
  }
  return sum;
}

console.log("123:", sumOfDigits(123));
console.log("9999:", sumOfDigits(9999));
console.log("-456:", sumOfDigits(-456));
console.log("1001:", sumOfDigits(1001));

Output

Problem 24: Find Average of Array Elements

Problem: Write a function to calculate the average (mean) of all numbers in an array.

Example

function findAverage(arr) { if (arr.length === 0) return 0; let sum = 0; for (let i = 0; i < arr.length; i++) { sum += arr[i]; } return sum / arr.length; } console.log("Average of [10, 20, 30, 40, 50]:", findAverage([10, 20, 30, 40, 50])); console.log("Average of [5, 15, 25]:", findAverage([5, 15, 25])); console.log("Average of [100]:", findAverage([100])); console.log("Average of [2, 4, 6, 8]:", findAverage([2, 4, 6, 8]));

Output

Average of [10, 20, 30, 40, 50]: 30
Average of [5, 15, 25]: 15
Average of [100]: 100
Average of [2, 4, 6, 8]: 5

Problem 25: Title Case a Sentence

Problem: Write a function that converts a sentence to title case (first letter of each word capitalized, rest lowercase).

Example

function toTitleCase(str) { let words = str.split(" "); let result = ""; for (let i = 0; i < words.length; i++) { let word = words[i].toLowerCase(); let capitalized = word[0].toUpperCase() + word.slice(1); if (i > 0) result += " "; result += capitalized; } return result; } console.log(toTitleCase("hello world")); console.log(toTitleCase("javaScript is FUN")); console.log(toTitleCase("PRACTICE MAKES PERFECT")); console.log(toTitleCase("the quick brown fox"));

Output

Hello World
Javascript Is Fun
Practice Makes Perfect
The Quick Brown Fox

Key Takeaways

Start simple — Variables, operators, and conditionals are the building blocks. Master them before moving to complex problems.

Loops are essential — Almost every problem involves iteration. Practice for, while, and do...while until they feel natural.

Functions make code reusable — Every solution above is wrapped in a function. This is a habit you must build early.

Strings and arrays share patterns — Reversing, searching, and counting use similar loop logic for both strings and arrays.

Edge cases matter — Zero, negative numbers, empty inputs — always think about what could break your code.

Read the output carefully — Before running any code, predict what it will print. This builds mental model accuracy.

Tips for Practice

Solve without looking at the solution first. Spend at least 10-15 minutes trying on your own.
Type the code, don't copy-paste. Typing builds muscle memory for syntax.
Modify each problem — change inputs, add edge cases, rewrite with different loop types.
Explain your solution out loud (rubber duck debugging). If you can explain it, you understand it.
Track your progress — mark which problems you solved without help and revisit the rest.
Practice daily — Even 2-3 problems per day builds strong fundamentals over a few weeks.
Use browser console — Open DevTools (F12) and test your code immediately.

Next Step: Once you've completed all 25 problems confidently, move on to the Intermediate Practice Set covering objects, higher-order functions, closures, and DOM manipulation.

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