Maps and Sets

Intro to Maps and Sets
Intro to Maps and Sets
Objects and arrays are common, but JavaScript also provides specialized data structures for certain jobs:
  • Map - key/value pairs with any key type
  • Set - a collection of unique values
These are great for lookups, caching, and deduplication.

Map - key/value lookups

const byId = new Map<string, { name: string }>()
byId.set('u1', { name: 'Ava' })
byId.set('u2', { name: 'Ben' })

const user = byId.get('u1')
// { name: 'Ava' }
Other useful methods:
byId.has('u2')
// true

byId.delete('u2')
// true

byId.size
// 1

Set - unique values

const tags = new Set(['typescript', 'data', 'typescript'])
const uniqueTags = [...tags]
// ['typescript', 'data']
Other useful methods:
tags.has('data')
// true

tags.add('arrays')

tags.delete('typescript')
// true

tags.size
// 2
JavaScript also has WeakMap and WeakSet for object keys that can be garbage-collected when nothing else references them. We'll just mention them in passing here, but they're useful for caching without memory leaks.
In this exercise, you'll use Map for fast lookup and Set for unique values.
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