Reflect.ownKeys()

The Reflect.ownKeys() static method returns an array of the target object's own property keys.

Syntax

Reflect.ownKeys(target)

Parameters

target
- : The target object from which to get the own keys.

Return value

An Array of the target object's own property keys, including strings and symbols. For most objects, the array will be in the order of:

Non-negative integer indexes in increasing numeric order (but as strings)
Other string keys in the order of property creation
Symbol keys in the order of property creation.

Exceptions

TypeError
- : Thrown if target is not an object.

Description

Reflect.ownKeys() provides the reflective semantic of retrieving all property keys of an object. It is the only way to get all own properties – enumerable and not enumerable, strings and symbols — in one call, without extra filtering logic. For example, Object.getOwnPropertyNames takes the return value of Reflect.ownKeys() and filters to only string values, while Object.getOwnPropertySymbols filters to only symbol values. Because normal objects implement OwnPropertyKeys to return all string keys before symbol keys, Reflect.ownKeys(target) is usually equivalent to Object.getOwnPropertyNames(target).concat(Object.getOwnPropertySymbols(target)). However, if the object has a custom OwnPropertyKeys method (such as through a proxy's ownKeys handler), the order of the keys may be different.

Reflect.ownKeys() invokes the OwnPropertyKeys object internal method of target.

Examples

Using Reflect.ownKeys()

Reflect.ownKeys({ z: 3, y: 2, x: 1 }); // [ "z", "y", "x" ]
Reflect.ownKeys([]); // ["length"]

const sym = Symbol.for("comet");
const sym2 = Symbol.for("meteor");
const obj = {
  [sym]: 0,
  str: 0,
  773: 0,
  0: 0,
  [sym2]: 0,
  "-1": 0,
  8: 0,
  "second str": 0,
};
Reflect.ownKeys(obj);
// [ "0", "8", "773", "str", "-1", "second str", Symbol(comet), Symbol(meteor) ]
// Indexes in numeric order,
// strings in insertion order,
// symbols in insertion order