Home Challenges Reps Problems Leaderboard Take a challenge

From SQL to JavaScript

Write one function that returns exactly what a GROUP BY query would. No loops.

Intermediate20 min on the clock5 graded checks · 100 pointsJavaScript + TypeScript

Graded by running your code against real cases.

What you build

WHERE: only completed orders above 100
GROUP BY country
Aggregate total_sales and order_count
ORDER BY total_sales descending
Leave the orders array exactly as you found it

Done means

The same rows, in the same order, as the SQL query would return.

How it is graded

Published in full, before you start — every point is one of these and there is nothing else. Each one runs your code; it is not a search for keywords.

WHERE — only completed orders above 100+15Array methods
GROUP BY — one row per country+20Array methods
Both aggregates are right+25Array methods
ORDER BY total_sales descending+20Array methods
The orders array comes back untouched+20Not mutating your inputs

What it teaches

Array methodsbeginner

map, filter, find and reduce replace almost every loop you would otherwise write — knowing which one returns what is the single highest-leverage thing in JavaScript.

Not mutating your inputsintermediate

sort() and reverse() change the array you gave them, which is how a filter quietly reorders the caller's data — copy first, and the bug never exists.

The rest of JavaScript + TypeScript

Product CatalogBeginner · 10 min Shopping CartBeginner · 15 min The Mutation TrapBeginner · 10 min API Data TransformationIntermediate · 12 min Search, Filter & SortIntermediate · 15 min PaginationBeginner · 12 min Async States & DebounceAdvanced · 20 min