# How to check if a JavaScript object property is undefined

> Learn the correct way to check if a JavaScript object property is undefined using the typeof operator, which returns the string undefined for missing values.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2018-05-26 | Updated: 2019-05-29 | Topics: [JavaScript](https://flaviocopes.com/tags/js/) | Canonical: https://flaviocopes.com/how-to-check-undefined-property-javascript/

In a [JavaScript](https://flaviocopes.com/javascript/) program, the correct way to check if an object property is undefined is to use the `typeof` operator.

`typeof` returns a string that tells the type of the operand. It is used without parentheses, passing it any value you want to check:

```js
const list = []
const count = 2

typeof list //"object"
typeof count //"number"
typeof "test" //"string"

typeof color //"undefined"
```

If the value is not defined, `typeof` returns the 'undefined' **string**.

Now suppose you have a `car` object, with just one property:

```js
const car = {
  model: 'Fiesta'
}
```

This is how you check if the `color` property is defined on this object:

```js
if (typeof car.color === 'undefined') {
  // color is undefined
}
```