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reject()

reject<T>(collection, predicate): T[]

reject<T>(collection, predicate): Partial<T>

The opposite of filter; this method returns the elements of collection that predicate does not return truthy for.

💎 Why is this a Hidden Gem?

The inverse of filter — exclude items instead of selecting them.

DEPRECATED

Use array.filter() with negated predicate or Object.entries().filter() directly instead.

Type Parameters​

T: T​

The type of elements in the array, or the object type.

Parameters​

Overload 1:

collection: T[]​

The collection to iterate over.

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

The function invoked per iteration.

Overload 2:

collection: T​

The collection to iterate over.

predicate: (value, key, object) => boolean​

The function invoked per iteration.

Returns: T[]​

The new filtered array or object.

See Also​

Since​

2.0.0

Also known as​

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

Example​

const numbers = [1, 2, 3, 4, 5];

// ❌ Deprecated approach
const oddNumbers = reject(numbers, n => n % 2 === 0);
console.log(oddNumbers); // [1, 3, 5]

// ✅ Recommended approach (for arrays)
const oddNumbersNative = numbers.filter(n => n % 2 !== 0);
console.log(oddNumbersNative); // [1, 3, 5]

// ✅ Recommended approach (for objects)
const obj = { a: 1, b: 2, c: 3 };
const oddValuesObj = Object.fromEntries(
  Object.entries(obj).filter(([, value]) => value % 2 !== 0)
);
console.log(oddValuesObj); // { a: 1, c: 3 }

How it works?​

Returns elements that do NOT pass the predicate (opposite of filter). Deprecated: Use array.filter() with negated predicate.

Native Equivalent​

// ❌ reject(arr, predicate)
// ✅ arr.filter(x => !predicate(x))

Use Cases​

Exclude items matching criteria 📌​

Filter out elements that match a condition.

const items = [{ active: true }, { active: false }, { active: true }];
items.filter(item => !item.active);
// => [{ active: false }]

Remove invalid entries​

Exclude items that fail validation.

const users = [{ email: "" }, { email: "a@b.com" }, { email: null }];
users.filter(u => u.email);
// => [{ email: "a@b.com" }]

Filter out completed tasks​

Get only pending tasks by excluding completed ones.

const tasks = [{ done: true }, { done: false }, { done: false }];
tasks.filter(t => !t.done);
// => [{ done: false }, { done: false }]