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JavaScript · Syntax · Beginner
Functions Level 2
20 tasks
Advanced JavaScript function practice: string and number handling, logical tests, arrays, filtering, counting, value searching, and writing reusable functions.
Quick topic start and explanations before exercises (exercises below):
At this level the functions are still small, but the logic requires combining several tools: loops, string methods, conditions, and return values. The challenge is deciding which tools to use.
Before writing the body, ask three questions: what type is the input, what type should come out, and what operation connects them?
For counting something in a string — vowels, letters, words — the pattern is: loop over the string, check each character, maintain a counter, return it.
```javascript
function countVowels(text) {
const vowels = "aeiouy";
let count = 0;
for (const char of text.toLowerCase()) {
if (vowels.includes(char)) {
count++;
}
}
return count;
}
```
text.toLowerCase() handles case before checking. vowels.includes(char) tests whether the character is in the vowel string.
For string transformations — reverse, remove characters, trim edges — JavaScript string methods often give you a clean one-liner:
```javascript
function reverseText(text) {
return text.split("").reverse().join("");
}
function removeSpaces(text) {
return text.split(" ").join("");
}
function trimEdges(text) {
return text.slice(1, -1);
}
```
split("").reverse().join("") is the idiomatic way to reverse a string in JavaScript: split into individual characters, reverse the array, join back. slice(1, -1) removes the first and last character — negative index in slice() counts from the end.
For numeric properties — last digit, absolute difference, divisibility:
```javascript
function lastDigit(n) {
return Math.abs(n) % 10;
}
function absDiff(a, b) {
return Math.abs(a - b);
}
function divisibleBy3And5(n) {
return n % 3 === 0 && n % 5 === 0;
}
```
Math.abs() is the JavaScript equivalent of Python's abs(). It handles negative inputs so the last digit of -47 is still 7, not -7.
A palindrome check compares the string to its reverse:
```javascript
function isPalindrome(text) {
return text === text.split("").reverse().join("");
}
```
Case sensitivity matters. "Racecar" reversed is "racecaR" — not equal. For production you would also strip spaces and convert to lowercase first. The exercises here test simple cases.
Counting words with split:
```javascript
function countWords(text) {
return text.trim().split(/\s+/).length;
}
```
split(/\s+/) splits on one or more whitespace characters and handles extra spaces. Without trim(), a leading space would create an empty first element.
Filtering and summing from an array:
```javascript
function sumPositive(numbers) {
let total = 0;
for (const n of numbers) {
if (n > 0) {
total += n;
}
}
return total;
}
```
Removing specific characters — iterate and rebuild:
```javascript
function removeExclamations(text) {
let result = "";
for (const char of text) {
if (char !== "!") {
result += char;
}
}
return result;
}
```
Alternatively with the replace method and a regex:
```javascript
function removeExclamations(text) {
return text.split("!").join("");
}
```
Both forms are valid. The loop is more readable for beginners; the split/join version is more idiomatic JavaScript.
Write a function that takes a string and returns it
in reversed form.
function reverseText(text) {
// your code here
}
Solution
function reverseText(text) {
return text.split('').reverse().join('');
}
// or like this using a loop
function reverseText(text) {
let result = "";
for (let char of text) {
result = char + result;
}
return result;
}
Write a function that takes a string and
returns the number of vowels in it.
Vowels: a, e, i, o, u, y (case does not matter).
function countVowels(text) {
// your code here
}
Solution
function countVowels(text) {
let vowels = "aeiouy";
let count = 0;
for (let ch of text.toLowerCase()) {
if (vowels.includes(ch)) {
count += 1;
}
}
return count;
}
Write a function that takes a string and
returns true if it is a palindrome.
function isPalindrome(text) {
// your code here
}
Solution
function isPalindrome(text) {
return text === text.split('').reverse().join('');
}
// or like this: prepare the reversed string separately
function isPalindrome(text) {
let reversed = text.split("").reverse().join("");
return text === reversed;
}
Write a function that takes a string and
returns the number of words in it.
Words are separated by spaces.
function countWords(text) {
// your code here
}
Solution
function countWords(text) {
if (text === "") {
return 0;
}
return text.trim() ? text.trim().split(/\s+/).length : 0;
}
// or like this: save the intermediate array of words into a variable
function countWords(text) {
let words = text.trim() ? text.trim().split(/\s+/) : [];
return words.length;
}
Write a function that takes two numbers and
returns their absolute difference.
function absDiff(a, b) {
// your code here
}
Solution
function absDiff(a, b) {
let diff = a - b;
if (diff < 0) {
diff = -diff;
}
return diff;
}
// or like this with Math.abs
function difference(a, b) {
return Math.abs(a - b);
}
Write a function that takes a number and
returns a string:
- "Small" — if the number is less than 10
- "Medium" — if it is from 10 to 100
- "Large" — if it is greater than 100
function sizeLabel(n) {
// your code here
}
Solution
function sizeLabel(n) {
if (n < 10) {
return "Small";
} else if (n <= 100) {
return "Medium";
} else {
return "Large";
}
}
Write a function that takes a string and
returns it without all exclamation marks "!".
function removeExclamations(text) {
// your code here
}
Solution
function removeExclamations(text) {
let result = "";
for (let ch of text) {
if (ch !== "!") {
result += ch;
}
}
return result;
}
// or like this with replaceAll
function removeExclamations(text) {
return text.replaceAll("!", "");
}
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