has()

has<T>(object, key): boolean

Checks if an object has a property as its own (not inherited).

note

Works with objects created via Object.create(null). Undefined/null values still return true if the property exists.

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Type Parameters

T: T extends object

The type of the object.

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Parameters

object: T

The object to check.

key: PropertyKey

The property key to check for.

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Returns: boolean

true if the object has the own property, false otherwise.

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See Also

Object.hasOwn (ES2022 native alternative)

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Since

2.0.0

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Performance

O(1) - Direct property lookup via Object.prototype.hasOwnProperty.

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Also known as

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

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Example

const obj = { a: 1, b: undefined };

has(obj, 'a'); // => true
has(obj, 'b'); // => true (property exists)
has(obj, 'c'); // => false

const bare = Object.create(null);
bare.x = 42;
has(bare, 'x'); // => true

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How it works?

Checks if an object has a property as its own (not inherited).

Own vs Inherited

Works with Object.create(null)

Unlike obj.hasOwnProperty(), has() works even when the prototype chain is broken.

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Use Cases

Check property existence 📌

Safely check if an object has a property as its own key (not inherited). Essential for robust validation against prototypes.

#check#property#existence#validation#own#hasOwnProperty

if (has(data, 'result')) {
  process(data.result);
}

Detect explicit undefined

Distinguish between a property that exists but is undefined vs a missing property. get() returns undefined in both cases, has() differentiates.

#detect#undefined#explicit#missing#differentiate#validation

const obj = { start: undefined };
has(obj, 'start'); // true
has(obj, 'end');   // false

Validate dynamic keys

Check for the presence of a key when the key name is variable. Useful in loops or dynamic logic.

#validate#dynamic#keys#variable#cache#lookup

const key = getCurrentKey();
if (!has(cache, key)) {
  loadData(key);
}