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differenceBy()

differenceBy<T>(array, values, iteratee): T[]

Creates an array of values from the first array that are not present in the second array, using an iteratee to compute the comparison value.

Type Parameters​

T: T​

The type of elements in the arrays.

Parameters​

array: readonly T[]​

The source array to filter.

values: readonly T[]​

The values to exclude.

iteratee: (item) => unknown | keyof T​

A function or property key to compute the comparison value.

Returns: T[]​

A new array containing elements whose computed values are not in values.

Since​

2.0.0

Performance​

O(n + m) time & space, uses hash map for constant-time lookups.

Also known as​

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

Example​

differenceBy([2.1, 1.2, 3.3], [2.3, 3.4], Math.floor);
// => [1.2]

differenceBy(
  [{ id: 1, name: 'Alice' }, { id: 2, name: 'Bob' }],
  [{ id: 2, name: 'Bobby' }],
  'id'
);
// => [{ id: 1, name: 'Alice' }]

How it works?​

Compares elements by a computed key (iteratee) instead of direct equality.

Use Cases​

Filter out duplicate objects by a specific property 📌​

Remove objects from an array based on a shared property value, not reference equality. Perfect for deduplicating user lists, filtering products, or managing unique entries.

const allUsers = [
  { id: 1, name: "Alice" },
  { id: 2, name: "Bob" },
  { id: 3, name: "Charlie" },
  { id: 4, name: "David" },
];
const bannedUsers = [
  { id: 2, name: "Bob" },
  { id: 4, name: "David" },
];

const activeUsers = differenceBy(allUsers, bannedUsers, "id");
// => [{ id: 1, name: "Alice" }, { id: 3, name: "Charlie" }]

Exclude items by computed value using a custom function​

Filter out elements based on a transformation or calculation result. Perfect for case-insensitive comparisons, date filtering, or normalized matching.

const allEmails = [
  "Alice@company.com",
  "BOB@company.com",
  "charlie@company.com",
];
const unsubscribed = ["alice@company.com", "bob@company.com"];

const activeEmails = differenceBy(allEmails, unsubscribed, (email) =>
  email.toLowerCase()
);
// => ["charlie@company.com"]

Filter items by derived date value using a custom function​

Exclude elements based on a computed temporal value like year, month, or quarter. Perfect for archiving old content, filtering reports by period, or managing time-based data.

const articles = [
  { title: "News 1", date: new Date("2024-03-15") },
  { title: "News 2", date: new Date("2025-01-10") },
  { title: "News 3", date: new Date("2024-07-22") },
];
const excludedYears = [{ date: new Date("2024-01-01") }];

const currentYearArticles = differenceBy(articles, excludedYears, (a) =>
  a.date.getFullYear()
);
// => [{ title: "News 2", date: 2025-01-10 }]