difference()

difference<T>(array, values): T[]

Creates an array of values from the first array that are not included in the second array.

remarque

Uses strict equality (===). Preserves duplicates from the source array.

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Type Parameters

T: T

The type of elements in the arrays.

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Parameters

array: readonly T[]

The source array to inspect.

values: readonly T[]

The array of values to exclude.

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Returns: T[]

A new array of filtered values.

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Since

2.0.0

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Performance

O(n·m) for small exclusion sets (≤16), O(n + m) with hash map for larger ones.

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Also known as

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

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Example

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

difference([1, 1, 2, 2, 3], [2]);
// => [1, 1, 3]

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How it works?

Returns elements from the first array that are not present in the exclusion array. Uses a Set for O(1) lookups.

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Use Cases

Filter out unwanted items from a list 📌

Remove specific elements from an array efficiently. Perfect for excluding blacklisted items, removing duplicates, or filtering selections.

#filter#remove#exclude#blacklist#unwanted#elements#filters

const allFruits = ["apple", "banana", "orange", "grape", "mango"];
const dislikedFruits = ["banana", "grape"];

const favoriteFruits = difference(allFruits, dislikedFruits);
// => ["apple", "orange", "mango"]

Sync available options after user selection 📌

Update available choices by removing already selected items from the pool. Perfect for multi-select forms, shopping carts, or team member assignments.

#sync#options#selection#choices#available#multi-select

const allPermissions = ["read", "write", "delete", "admin", "export"];
const alreadyGranted = ["read", "write"];

const availablePermissions = difference(allPermissions, alreadyGranted);
// => ["delete", "admin", "export"]

Detect new entries in a dataset

Compare two snapshots to find newly added elements. Perfect for tracking new users, detecting file changes, or monitoring inventory updates.

#detect#new#entries#compare#snapshots#changes#tracking#ci/cd

const previousUsers = ["alice", "bob", "charlie"];
const currentUsers = ["alice", "bob", "charlie", "david", "emma"];

const newUsers = difference(currentUsers, previousUsers);
// => ["david", "emma"]

Detect missing permissions for access control

Compare required permissions against granted ones to identify gaps. Essential for role-based access control and security audit systems.

#permissions#missing#access#control#authorization#RBAC#security#a11y

const requiredPermissions = ["read", "write", "deploy", "audit"];
const userPermissions = ["read", "write"];

const missingPermissions = difference(requiredPermissions, userPermissions);
// => ["deploy", "audit"]

if (missingPermissions.length > 0) {
  throw new Error(`Missing permissions: ${missingPermissions.join(", ")}`);
}

Find missing dependencies in a project

Compare required packages against installed ones to detect missing dependencies. Useful for CI pipelines, project scaffolding, and dependency audit tools.

#dependencies#missing#imports#tooling#package#audit#CI#ci/cd#scripts

const requiredPackages = ["react", "react-dom", "typescript", "vitest", "eslint"];
const installedPackages = ["react", "react-dom", "typescript"];

const missingPackages = difference(requiredPackages, installedPackages);
// => ["vitest", "eslint"]

console.log(`Install missing: pnpm add -D ${missingPackages.join(" ")}`);

Implement "Deselect All" by removing category items

Remove all items from a category from the current selection. Essential for "Deselect All" in data tables and multi-select components.

#deselect#selection#model#checkbox#table#design system#a11y

const currentSelection = ["item-1", "item-2", "item-3", "item-4", "item-5"];
const categoryItems = ["item-2", "item-3", "item-4"];

// Deselect category: remove category items from selection
const afterDeselect = difference(currentSelection, categoryItems);
// => ["item-1", "item-5"]

updateSelectionState(afterDeselect);

Compute hidden columns in a data table

Find which columns are hidden by comparing all columns against visible ones. Essential for column visibility toggles in data table components.

#columns#hidden#visible#table#data#design system#panels

const allColumns = ["name", "email", "role", "status", "lastLogin", "createdAt"];
const visibleColumns = ["name", "email", "status"];

const hiddenColumns = difference(allColumns, visibleColumns);
// => ["role", "lastLogin", "createdAt"]

renderColumnToggle(allColumns, hiddenColumns);

Find unread notifications

Identify notifications the user hasn't seen yet. Essential for notification badges and unread indicators.

#unread#notifications#read#tracking#inbox#design system

const allNotificationIds = ["n1", "n2", "n3", "n4", "n5"];
const readIds = ["n1", "n3"];

const unreadIds = difference(allNotificationIds, readIds);
// => ["n2", "n4", "n5"]

setBadgeCount(unreadIds.length); // Show "3" on bell icon

Detect removed items between config versions

Compare two config versions to find removed keys for migration warnings. Perfect for CLI tools, config validators, and upgrade scripts.

#removed#config#diff#migration#scripts#ci/cd#observability

const previousKeys = ["apiUrl", "timeout", "retries", "legacyMode", "debugLevel"];
const currentKeys = ["apiUrl", "timeout", "retries", "logLevel"];

const removedKeys = difference(previousKeys, currentKeys);
// => ["legacyMode", "debugLevel"]

if (removedKeys.length > 0) {
  console.warn(`Deprecated config keys detected: ${removedKeys.join(", ")}`);
}