Object.keys()
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
The Object.keys() static method returns an array of a given object's own enumerable string-keyed property names.
Try it
const object = {
a: "some string",
b: 42,
c: false,
};
console.log(Object.keys(object));
// Expected output: Array ["a", "b", "c"]
Syntax
Object.keys(obj)
Parameters
obj-
An object.
Return value
An array of strings representing the given object's own enumerable string-keyed property keys.
Description
Object.keys() returns an array whose elements are strings corresponding to the enumerable string-keyed property names found directly upon object. This is the same as iterating with a for...in loop, except that a for...in loop enumerates properties in the prototype chain as well. The order of the array returned by Object.keys() is the same as that provided by a for...in loop.
If you need the property values, use Object.values() instead. If you need both the property keys and values, use Object.entries() instead.
Examples
Using Object.keys()
// Basic array
const arr = ["a", "b", "c"];
console.log(Object.keys(arr)); // ['0', '1', '2']
// Array-like object
const obj = { 0: "a", 1: "b", 2: "c" };
console.log(Object.keys(obj)); // ['0', '1', '2']
// Array-like object with random key ordering
const anObj = { 100: "a", 2: "b", 7: "c" };
console.log(Object.keys(anObj)); // ['2', '7', '100']
// getFoo is a non-enumerable property
const myObj = Object.create(
{},
{
getFoo: {
value() {
return this.foo;
},
},
},
);
myObj.foo = 1;
console.log(Object.keys(myObj)); // ['foo']
If you want all string-keyed own properties, including non-enumerable ones, see Object.getOwnPropertyNames().
Using Object.keys() on primitives
Non-object arguments are coerced to objects. undefined and null cannot be coerced to objects and throw a TypeError upfront. Only strings may have own enumerable properties, while all other primitives return an empty array.
// Strings have indices as enumerable own properties
console.log(Object.keys("foo")); // ['0', '1', '2']
// Other primitives except undefined and null have no own properties
console.log(Object.keys(100)); // []
Note:
In ES5, passing a non-object to Object.keys() threw a TypeError.
Specifications
| Specification |
|---|
| ECMAScript® 2027 Language Specification # sec-object.keys |
Browser compatibility
| desktop | mobile | server | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
keys
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Legend
Tip: you can click/tap on a cell for more information.
- Full support
- Full support