Arrays and Sets in Javascript

Array, Object, Set, Map

what are they?

also

speed concerns

• Set vs Object
  • Set is twice as fast as Object
• Map vs Array
  • Generally faster than Array (refer to below cheatsheet)

*a collection is a "list" of stuff, in the english sense of the word. an Array of names is a collection of names.

cheatsheet ref

When to use Arrays

• when you need to iterate something
• when you don't

When to use Objects

• when you want to store key value pairs
• when the same person tells you to do the same operation n-times for random id in your array

When to use Sets

• set union / intersection / difference
• is an object in set?
• iterate over set, knowing everything is unique
• turn arrays into unique sets (like a normal use case in python)

When to use WeakSets

• when All you want to get is one bit of information: Is the object (or generically, value) contained in the set?
• tag objects without mutating them
• https://esdiscuss.org/topic/actual-weakset-use-cases
• https://stackoverflow.com/questions/30556078/ecmascript-6-what-is-weakset-for

When to use Maps

• for fast searching and looking up data. ref
• for adding items to and removing items from the map. ref

When to use WeakMaps

// delete private data when user is gone
export let USER_1 = { name: 'John' }

const metadata = new WeakMap()
  .set(USER_1, {
    currentLocation: '...',
    personallyIdentifiableInformation: '...',
  })
  .set(/*...*/)

// somewhere down the line...

// user logout
USER_1 = null

• keep an object’s private data private
• used to keep track of DOM nodes/objects.
• https://stackoverflow.com/questions/29413222/what-are-the-actual-uses-of-es6-weakmap
• https://www.mattzeunert.com/2017/01/31/weak-maps.html

note from v8

from v8.dev:

JavaScript objects mostly behave like dictionaries, with string keys and arbitrary objects as values. The specification does however treat integer-indexed properties and other properties differently during iteration. Other than that, the different properties behave mostly the same, independent of whether they are integer indexed or not.

further reading

• https://codeburst.io/array-vs-set-vs-map-vs-object-real-time-use-cases-in-javascript-es6-47ee3295329b
• https://adrianmejia.com/data-structures-time-complexity-for-beginners-arrays-hashmaps-linked-lists-stacks-queues-tutorial/
• https://javascript.info/weakmap-weakset