---
title: What's the difference between undeclared, undefined and null in JavaScript?
type: question
tags: javascript,type
authors: chalarangelo
cover: blog_images/river-houses.jpg
excerpt: JavaScript has three different empty states for variables. Learn their differences and how you can check for each one.
---

### undeclared

A variable is undeclared if it has not been declared with an appropriate keyword (i.e. `var`, `let` or `const`). Accessing an undeclared variable will throw a `ReferenceError`.

```js
console.log(x); // ReferenceError: x is not defined
```

### undefined

A variable is `undefined` if it hasn't been assigned a value. `undefined` is a primitive data type in JavaScript and represents the absence of a value, intentional or otherwise.

```js
let x;
console.log(x); // undefined
```

### null

A variable is assigned a value of `null` like any other value. `null` is also primitive data type in JavaScript and always represents the intentional absence of a value.

```js
let x = null;
console.log(x); // null
```

### Checking for empty states

Undeclared variables will throw an error, which makes them easy to spot and are not very common anyways. `undefined` and `null` can be easily spotted with a conditional as they are both falsy values. Due to that, `null` and `undefined` are loosely equal (`==`), but not strictly equal (`===`).

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