# How to check if a variable is undefined or NULL in JavaScript

By Atta Ur Rehman Shah (https://attacomsian.com/about). Published Sep 17, 2022. Topics: JavaScript.
Canonical URL: https://attacomsian.com/blog/javascript-check-if-variable-is-undefined-or-null

> Learn how to use the equality operator == to check if a variable is undefined or null in JavaScript. 

To check if a variable is `undefined` or `null` in JavaScript, either use the equality operator `==` or strict equality operator `===`. 

In JavaScript, a variable is considered `undefined` if it is declared but not assigned a value. Whereas the `null` is a special assignment value that signifies 'no value' or nonexistence of any value:

```javascript
let name
let age = null

console.log(name)    // undefined
console.log(age)     // null
```

The equality operator `==` (also called loose equality operator) provides a more concise way to check whether the variable is `undefined` or `null`:

```javascript
let name // undefined variable

if (name == null) {
  console.log(`Name is either undefined or null`)
} else {
  console.log(`Name is NOT undefined or null`)
}

// Output => Name is either undefined or null
```

The condition `name == null` evaluates to `true` because the equality operator treats both `undefined` and `null` as the same:

```javascript
console.log(null == undefined) // true
```

Since the strict equality operator `===` (also called identity operator) does not treat `undefined` and `null` as the same, we have to use the `||` (or) operator to check if either of the two conditions is met:

```javascript
let name

if (name === undefined || name === null) {
  console.log(`Name is either undefined or null`)
} else {
  console.log(`Name is NOT undefined or null`)
}

// Output => Name is either undefined or null
```

The strict equality operator `===` is more explicit but less concise as compared to the loose equality operator `==` for checking if the variable is `undefined` or `null` in JavaScript.