List Keys
Object.keys returns an array of an object's own enumerable keys.
It is useful for iteration and validation.
JavaScript Tutorial
JavaScript Object.keys()
Object.keys returns an array of an object's own enumerable property names.
It is commonly used for iteration and validation.
Why We Need It
When working with objects, you often need to list keys for loops or checks.
Object.keys makes that simple and reliable.
Syntax
Object.keys(obj)Basic Example
1. Basic keys
const user = { name: "Ava", role: "admin" };
const keys = Object.keys(user);
console.log(keys);Returns ['name', 'role'].
Real World Example
2. Iterate
const settings = { theme: "dark", layout: "grid" };
Object.keys(settings).forEach((key) => {
console.log(key, settings[key]);
});Loop over keys to access values.
Multiple Use Cases
Pairs with values and entries
Use Object.values for values and Object.entries for key-value pairs.
Together they cover most inspection use cases.
Non-Objects
Object.keys works on arrays too, returning index strings.
It ignores properties in the prototype chain.
More Examples
Comparison
Without
for (const key in obj) {
if (Object.hasOwn(obj, key)) {
console.log(key);
}
}With
Object.keys(obj).forEach((key) => console.log(key));Common Mistakes and Fixes
Expecting inherited keys
Object.keys returns only own enumerable properties.
Using keys for values
Use Object.values when you only need values.
Assuming numeric order
Key order exists but should not be relied on for logic.
Interview Questions
What does Object.keys return?
An array of own enumerable keys.
Does it include inherited keys?
No, only own properties.
Why use Object.keys over for...in?
It avoids inherited properties without extra checks.
Practice Problem
Practice: Count how many properties an object has using Object.keys.
const user = { name: "Ava", role: "admin" };
// TODO: count keys
One Possible Solution
const user = { name: "Ava", role: "admin" };
const count = Object.keys(user).length;
console.log(count);Frequently Asked Questions
What does Object.keys return?
An array of own enumerable property names.
Does it include inherited properties?
No, only own properties.
Can I use it on arrays?
Yes, it returns string indexes.
Try It Yourself
Try adding properties and see how the key list changes.