miku86

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# JavaScript Katas: Count lowercase letters

## Intro π

Problem solving is an important skill, for your career and your life in general.

That's why I take interesting katas of all levels, customize them and explain how to solve them.

## Understanding the Exerciseβ

First, we need to understand the exercise!
If you don't understand it, you can't solve it!.

My personal method:

1. Input: What do I put in?
2. Output: What do I want to get out?

### Today's exercise

Source: Codewars

Write a function `amountOfLowercaseLetters`, that accepts one parameter: `inputString`.

Given a string, e.g. `"aB1c"`,
return the number of lowercase letters in this string, e.g. `2`:

Input: a string.

Output: a number.

## Thinking about the Solution π­

I think I understand the exercise (= what I put into the function and what I want to get out of it).

Now, I need the specific steps to get from input to output.

I try to do this in small baby steps.

1. Loop over every character
2. Check if it is a lowercase letter
3. If yes, then increase count of lowercase letters by 1
4. Return count of lowercase letters

Example:

• Input: `"aB1c"`
• Iteration 1: lowercase letter? `true` => Increase count of lowercase letters by 1
• Iteration 2: lowercase letter? `false` => Do nothing
• Iteration 3: lowercase letter? `false` => Do nothing
• Iteration 4: lowercase letter? `true` => Increase count of lowercase letters by 1
• Output: `2` (count of lowercase letters) β

## Implementation (for) β

``````function amountOfLowercaseLetters(inputString) {
let count = 0;

// loop over every char
for (const char of inputString) {
// check if it is lowercase
if (char.match(/[a-z]/)) {
// if yes, increase count
count += 1;
}
}

return count;
}
``````

### Result

``````console.log(amountOfLowercaseLetters("aB1c"));
// 2 β

console.log(amountOfLowercaseLetters("123"));
// 0 β
``````

## Implementation (functional) β

``````function amountOfLowercaseLetters(inputString) {
return inputString
.split("") // convert into array
.filter((char) => char.match(/[a-z]/)) // filter out all lowercase chars
.length; // take the length
}
``````

### Result

``````console.log(amountOfLowercaseLetters("aB1c"));
// 2 β

console.log(amountOfLowercaseLetters("123"));
// 0 β
``````

## Implementation (global regex) β

``````function amountOfLowercaseLetters(inputString) {
return (inputString.match(/[a-z]/g) || []).length;
}
``````

We use the `g` flag to return all matches. Because `null` would get returned if there wouldn't be a match, we add an `[]` to use `length`.

### Result

``````console.log(amountOfLowercaseLetters("aB1c"));
// 2 β

console.log(amountOfLowercaseLetters("123"));
// 0 β
``````

## Playground β½

You can play around with the code here

## Next Part β‘οΈ

Great work!

We learned how to use `for of`, `match`, `filter` and `length`.

I hope that you can use your new learnings to solve problems more easily!

Next time, we'll solve another interesting kata. Stay tuned!

If I should solve a specific kata, shoot me a message here.

If you want to read my latest stuff, get in touch with me!

## Questions β

• How often do you do katas?
• Which implementation do you like more? Why?
• Any alternative solution?