Sum two numbers

Step 1 of 6

Return the sum of two numbers.
The simplest function, just to warm up.

Instructions

In script.js:

Find the addNumbers stub.
Return a + b.
Use return, not console.log.

Hints

One line: return a + b;.

Refresher: JS Functions.

How it works

Capitalize the first letter

Step 2 of 6

Return s with the first letter upper-cased.
Example: "kai" becomes "Kai".

Instructions

In script.js:

Capitalize the first character with s.charAt(0).toUpperCase().
Append the remaining characters with s.slice(1).
Return the two parts concatenated with +.

Hints

Edge case: if s is empty, return "" so the helper does not crash.

Strings have a .toUpperCase() method.

See JS String Methods.

How it works

Reverse a string

Step 3 of 6

Return s with its characters in reverse order.
Example: "hello" becomes "olleh".

Instructions

In script.js:

Start with let result = "".
Loop with for (let i = s.length - 1; i >= 0; i--).
Inside the loop, write result += s.charAt(i).
Return result.

Hints

The point is the for loop.

Do not use .split("").reverse().join("").

How it works

Check for a palindrome

Step 4 of 6

Return true if s reads the same forwards and backwards.
Case-insensitive.

Instructions

In script.js:

Lower-case s first with const lower = s.toLowerCase().
Compare it with its reverse by reusing reverseString.
Return the boolean result of the comparison.

Hints

Edge case: an empty string reads the same forwards and backwards, so it returns true naturally.

You can call your own helpers.

Example: return lower === reverseString(lower);.

How it works

Count the vowels

Step 5 of 6

Return how many vowels are in s.
Count both upper and lower case.

Instructions

In script.js:

Start with let count = 0.
Loop with for (let i = 0; i < s.length; i++).
For each character, check "aeiouAEIOU".indexOf(s.charAt(i)) !== -1.
If true, run count++.
Return count.

Hints

indexOf returns -1 when the character is not in the lookup string.

How it works

Render results

Step 6 of 6

Wire it all up.
Fill in init() so each function result shows up on the page.

Instructions

In script.js:

Inside init(), read each input constant at the top of the file.
Call each helper and write the result to its target with textContent.
addNumbers writes to #r-add.
capitalize writes to #r-cap.
reverseString writes to #r-rev.
isPalindrome writes to #r-pal.
countVowels writes to #r-vow.

Hints

Use document.getElementById("r-add").textContent = String(addNumbers(NUM_A, NUM_B));.

See DOM textContent.

How it works