Blog - javascript coding challenges

JavaScript's Past, Present, & Performance

Hello, checkiomates🐱‍👤!

This week's digest reflects on Chrome's history, masters text manipulation with a modern API, and revisits the fundamentals of Big O notation. Our mission applies logical analysis to a real-world pricing problem.

💡TIP

At every mission page, under the editor window, there is a terminal window.
If you want to discover all CheckiO features, visit our tutorial. It's a longread, but it's worth it!

🏁MISSION

Price Research by freeman_lex -

A journalist collected data on the prices of alcohol and gasoline in several states for a report on the economic advantage of filling up with alcohol. The rule used is that alcohol is considered advantageous when its price per liter is at most 70% of the price per liter of gasoline. Given the prices collected, your program must identify in which states it is more advantageous to fill up with alcohol. If it is not advantageous to use alcohol in any state, return a list with single element "*".

assert.deepStrictEqual(
    filterRegions([
        ["AM", 7.0, 10.0],
        ["RS", 7.01, 10.0],
    ]),
    ["AM"],
);
assert.deepStrictEqual(
    filterRegions([
        ["SP", 4.9, 5.8],
        ["RJ", 4.7, 5.7],
        ["PR", 4.6, 5.6],
    ]),
    ["*"],
);

📖ARTICLES

Google Chrome at 17 - A history of our browser -

A fantastic walkthrough of Chrome’s origins and its evolution over the years. Addy looks at key milestones (multi-process architecture for example), security, its steps into the world of AI, and more.

Accurate text lengths with `Intl.Segmenter` -

A useful tip for when .length just isn’t returning what you’d quite expect..

An Illustrated Guide to Big O and Time Complexity -

A fantastic JavaScript-oriented, interactive, visual essay about Big O notation and its role in describing algorithmic complexity. This is a beautiful bit of work, even if you’re already wise to O(log n) and O(n^2).

👩‍💻CODE SHOT

What do you think the following code does?

function checkio(items: Boolean[]): boolean {

    return items.filter(x => x==true).length > items. Length/2;
}

🙌 Thanks for your attention! Hope to meet you at CheckiO, as well as at our Instagram and Twitter! We are really interested in your thoughts! Please, leave a comment below! ⤵

Created: Sept. 10, 2025, 6:14 p.m.

freeman_lex