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Product Catalog

Five lookups over a product list. This is map, filter, find and reduce, and nothing else.

Beginner10 min on the clock6 graded checks · 100 pointsJavaScript + TypeScript

Graded by running your code against real cases.

What you build

getProductById(id) — the product, or undefined if there is none
getProductsByCategory(category) — every product in that category
getProductsAbovePrice(price) — strictly above, not equal
getTotalInventoryValue() — the sum of every price
getMostExpensiveProduct() — the single dearest product

Done means

Every function returns the right value, including for inputs that match nothing.

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.

getProductById finds one, and copes with a miss+20Array methods
getProductsByCategory returns every match+20Array methods
getProductsAbovePrice excludes the boundary+15Array methods
getTotalInventoryValue sums with reduce+20Array methods
getMostExpensiveProduct picks the dearest+15Array methods
None of them reorder the original list+10Not 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

Shopping CartBeginner · 15 min The Mutation TrapBeginner · 10 min From SQL to JavaScriptIntermediate · 20 min API Data TransformationIntermediate · 12 min Search, Filter & SortIntermediate · 15 min PaginationBeginner · 12 min Async States & DebounceAdvanced · 20 min