Object.keys()

Object.keys(obj)

Returns: Array · Updated March 13, 2026 · Object Methods

javascript object keys enumerable

Object.keys() returns an array of a given object’s own enumerable string-keyed property names, in the same order as a for...in loop (except for...in also enumerates inherited properties).

Syntax

Object.keys(obj)

Parameters

Parameter	Type	Default	Description
obj	Object	required	The object whose own enumerable string-keyed property names are to be returned.

Return Value

An array of strings representing the given object’s own enumerable string-keyed property names.

Examples

Basic usage

const obj = { a: 1, b: 2, c: 3 };

console.log(Object.keys(obj));
// ['a', 'b', 'c']

With an array

const arr = ['a', 'b', 'c'];

console.log(Object.keys(arr));
// ['0', '1', '2']

Order of keys

const obj = { 10: 'ten', 1: 'one', 2: 'two' };

console.log(Object.keys(obj));
// ['1', '2', '10'] — numeric keys sorted, then string keys in insertion order

Non-enumerable properties are excluded

const obj = Object.create({}, {
  hidden: { value: 'secret', enumerable: false },
  visible: { value: 'public', enumerable: true }
});

console.log(Object.keys(obj));
// ['visible']

Primitive values are coerced

Object.keys('hello');
// ['0', '1', '2', '3', '4']

Object.keys(42);
// []

Object.keys(null);
// throws TypeError

Common Patterns

Iterating over object properties

const user = { name: 'Alice', age: 30, role: 'admin' };

Object.keys(user).forEach(key => {
  console.log(`${key}: ${user[key]}`);
});
// name: Alice
// age: 30
// role: admin

Checking if an object is empty

function isEmpty(obj) {
  return Object.keys(obj).length === 0;
}

console.log(isEmpty({}));       // true
console.log(isEmpty({ a: 1 })); // false

Transforming keys

const original = { firstName: 'Alice', lastName: 'Smith' };

const snakeCase = Object.keys(original).reduce((acc, key) => {
  const snakeKey = key.replace(/([A-Z])/g, '_$1').toLowerCase();
  acc[snakeKey] = original[key];
  return acc;
}, {});

console.log(snakeCase);
// { first_name: 'Alice', last_name: 'Smith' }