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intersection()

intersection<T>(...arrays): T[]

Computes the intersection of multiple arrays.

This function takes multiple arrays and returns a new array containing only the elements that are present in all input arrays.

Type Parameters​

T: T​

The type of the elements in the input arrays.

Parameters​

arrays: ...readonly (readonly T[])[]​

Arrays of type T to compute the intersection from.

Returns: T[]​

A new array containing the common elements found in all input arrays.

Since​

2.0.0

Performance​

O(n × m) time & space where n = first array length, m = number of arrays. Uses Set for constant-time lookups.

Also known as​

intersection (Lodash, es-toolkit, Remeda, Ramda, Effect, Modern Dash) · intersects (Radashi) · ❌ (Antfu)

Example​

intersection([1, 2, 3], [2, 3, 4], [3, 4, 5]);
// => [3]

intersection(['a', 'b'], ['b', 'c'], ['b', 'd']);
// => ['b']

How it works?​

Returns elements that exist in ALL input arrays. Uses Set for O(1) membership testing.

Use Cases​

Find common permissions across user roles 📌​

Identify shared access rights between multiple roles or user groups. Perfect for permission systems, access control, or role-based authorization.

const adminPermissions = ["read", "write", "delete", "admin", "audit"];
const editorPermissions = ["read", "write", "publish", "audit"];
const viewerPermissions = ["read", "comment", "audit"];

const commonPermissions = intersection(
  adminPermissions,
  editorPermissions,
  viewerPermissions
);
// => ["read", "audit"]

Filter available time slots for scheduling​

Find overlapping availability across multiple participants for meetings. Ideal for calendar apps, booking systems, or team scheduling tools.

const aliceSlots = ["09:00", "10:00", "11:00", "14:00", "15:00"];
const bobSlots = ["10:00", "11:00", "13:00", "14:00", "16:00"];
const charlieSlots = ["08:00", "10:00", "14:00", "15:00", "17:00"];

const availableForAll = intersection(aliceSlots, bobSlots, charlieSlots);
// => ["10:00", "14:00"]

Identify common tags across items​

Find shared attributes between products, articles, or any tagged entities. Useful for recommendation engines, filtering systems, or content analysis.

const article1Tags = ["javascript", "typescript", "react", "frontend"];
const article2Tags = ["typescript", "nodejs", "backend", "react"];
const article3Tags = ["react", "typescript", "testing", "jest"];

const commonTags = intersection(article1Tags, article2Tags, article3Tags);
// => ["typescript", "react"]

Resolve active feature flags for a user​

Find which features are enabled for a user by intersecting their segments with active flags. Essential for feature flag systems, gradual rollouts, and A/B testing platforms.

const userSegments = ["beta-testers", "premium", "eu-region"];
const betaFeatures = ["new-dashboard", "ai-search"];
const premiumFeatures = ["ai-search", "export-pdf", "priority-support"];
const euFeatures = ["gdpr-banner", "cookie-consent", "ai-search"];

// Features available to ALL of the user's segments
const universalFeatures = intersection(betaFeatures, premiumFeatures, euFeatures);
// => ["ai-search"]

Determine which filter values remain valid when multiple filters are combined. Critical for e-commerce product filtering where options narrow down as filters are applied.

// Products available in size "M"
const sizeMColors = ["red", "blue", "green", "black"];
// Products available in brand "Nike"
const nikeColors = ["blue", "black", "white"];
// Products available under $50
const budgetColors = ["red", "blue", "black", "yellow"];

// Colors available for: size M + Nike + under $50
const availableColors = intersection(sizeMColors, nikeColors, budgetColors);
// => ["blue", "black"]