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takeRightWhile()

takeRightWhile<T>(array, predicate): T[]

Creates a slice of array with elements taken from the end while predicate returns truthy.

Type Parameters​

T: T​

The type of elements in the array.

Parameters​

array: readonly T[]​

The array to query.

predicate: (value, index, array) => boolean​

The function invoked per iteration.

Returns: T[]​

A new array of taken elements.

Since​

2.0.0

Performance​

O(n) time, stops at first falsy predicate result from end.

Also known as​

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

Example​

const users = [
  { user: 'barney', active: false },
  { user: 'fred', active: true },
  { user: 'pebbles', active: true }
];

takeRightWhile(users, u => u.active);
// => [{ user: 'fred', active: true }, { user: 'pebbles', active: true }]

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

How it works?​

Takes elements from the end while predicate is true. Scans from right to left.

Use Cases​

Get trailing valid entries 📌​

Take elements from the end while they pass a condition. Perfect for extracting suffixes or recent valid sequences.

const data = [1, 2, -1, 3, 4, 5];

const validSuffix = takeRightWhile(data, (n) => n > 0);
// => [3, 4, 5]

Extract recent completed tasks​

Get trailing items that match a status. Useful for showing "recently completed" or latest successes.

const tasks = [
  { status: "pending", name: "Task 1" },
  { status: "done", name: "Task 2" },
  { status: "done", name: "Task 3" },
  { status: "done", name: "Task 4" },
];

const recentlyCompleted = takeRightWhile(tasks, (t) => t.status === "done");
// => [Task 2, Task 3, Task 4]

Get trailing positive values​

Extract suffix of values above a threshold. Perfect for trend analysis or recent performance extraction.

const metrics = [-5, 10, -2, 15, 20, 25];

const recentGrowth = takeRightWhile(metrics, (m) => m > 0);
// => [15, 20, 25]

Extract recent unread notifications​

Take trailing unread notifications for a notification badge count. Perfect for notification centers and inbox indicators.

const notifications = [
  { id: 1, read: true, text: "Welcome" },
  { id: 2, read: true, text: "New feature" },
  { id: 3, read: false, text: "New comment" },
  { id: 4, read: false, text: "New follower" },
  { id: 5, read: false, text: "Mention in #general" },
];

const recentUnread = takeRightWhile(notifications, (n) => !n.read);
// => [New comment, New follower, Mention]

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