Set Methods for JavaScript

This is a proposal to add methods like union and intersection to JavaScript's built-in Set class.

It is currently at stage 4: it has been added to the specification. This repository is no longer active.

Original readme follows.

Proposal

This would add the following methods:

• Set.prototype.intersection(other)
• Set.prototype.union(other)
• Set.prototype.difference(other)
• Set.prototype.symmetricDifference(other)
• Set.prototype.isSubsetOf(other)
• Set.prototype.isSupersetOf(other)
• Set.prototype.isDisjointFrom(other)

These methods would all require their arguments to be a Set, or at least something which looks like a Set in terms of having a numeric size property as well as keys and has methods.

See details.md for details of current decisions made in this proposal.

Rendered spec text is available here.

The proposal was originally authored by Michał Wadas and later championed by Sathya Gunasekaran and Kevin Gibbons.

Implementations

This proposal is ready for engines to implement and ship. See this issue for current status.

TC39 meeting notes

• May 2018
• January 2019
• March 2022 - discussion of how to extend built-ins in general
• July 2022
• September 2022
• November 2022
• March 2023
• July 2023
• February 2024
• April 2024

(Semi)relevant previous discussions

• proposal-rm-builtin-subclassing
• Map#map and Map#filter
• Map.prototype.map and Map.prototype.filter (spec) + Set
• Map: filter/map and more
• Original topic regarding this proposal
• Newer topic regarding this proposal

Comparison with other languages

See other languages document to get overview of Set methods in other languages.

Naming

See naming bikeshedding document for details.

We decided to choose:

• Symmetric difference - symmetricDifference
• Intersection - intersection
• Union - union
• Difference - difference

Polyfills

• core-js
• es-shims:
  • difference
  • intersection
  • symmetricDifference
  • union
  • isDisjointFrom
  • isSubsetOf
  • isSupersetOf