03-map

Exercise 03 - Map

The scenario

Raw data from the park's sensors is never in the shape the dashboard needs. Numbers need doubling for calibration, dinosaur records need flattening to just their names for a dropdown menu, and full sighting records need formatting into human-readable log lines.

You'll use .map() to transform arrays - taking one shape of data in and producing a new array of a different shape, without mutating the original.

What you will build

All functions live in starter/mappers.js.

Function	Description	Example
doubleAll(numbers)	Return a new array with every number doubled	doubleAll([1,2,3]) → [2,4,6]
extractNames(dinos)	Return an array of just the species strings	extractNames([{species:'Rex',...}]) → ['Rex']
formatSightings(dinos)	Return formatted strings like "Rex (North) - danger: 9"	One string per dino

Each dino is { species: string, zone: string, dangerLevel: number }.

Getting started

Open starter/mappers.js. Replace the stubs with .map() calls. Then run:

node starter/index.js

Verify

cd starter && pnpm install && pnpm test

The tests check empty arrays, negative numbers, species extraction, and the exact format string for sightings.

Hints

• .map() returns a new array of the same length - the callback transforms each element.
• For extractNames, you just need to pull one property: d => d.species.
• Template literals make formatSightings clean: `${d.species} (${d.zone}) - danger: ${d.dangerLevel}`.

Reference solution

solution/mappers.js