New JavaScript Set Methods: union, intersection and difference

JavaScript has had Set since ES2015, but combining sets meant converting to arrays and filtering. ES2025 added the classic set operations as methods.

The operations

const frontend = new Set(['asha', 'ravi', 'meera']);
const oncall   = new Set(['ravi', 'kiran']);

frontend.union(oncall);               // Set {'asha', 'ravi', 'meera', 'kiran'}
frontend.intersection(oncall);        // Set {'ravi'}
frontend.difference(oncall);          // Set {'asha', 'meera'}
frontend.symmetricDifference(oncall); // Set {'asha', 'meera', 'kiran'}

Comparisons

const required = new Set(['read', 'write']);
const granted  = new Set(['read', 'write', 'delete']);

required.isSubsetOf(granted);      // true: user has every required permission
granted.isSupersetOf(required);    // true
required.isDisjointFrom(new Set(['admin'])); // true: nothing in common

Real-world examples

// Which selected rows are new since last save?
const added = new Set(selectedIds).difference(new Set(savedIds));
const removed = new Set(savedIds).difference(new Set(selectedIds));

// Tags shared by two articles
const shared = new Set(a.tags).intersection(new Set(b.tags));

// Feature access check
const canPublish = new Set(['write', 'publish']).isSubsetOf(user.permissions);

Details

• All methods return new sets; the originals aren't changed.
• The argument can be any "set-like" object with size, has() and keys(), including a Map.
• Use [...set] or Array.from(set) when you need an array back.
• Available in current versions of all major browsers and Node.js 22+.