/JavaScript

# Logical NOT (!)

The logical NOT (`!`) operator (logical complement, negation) takes truth to falsity and vice versa. It is typically used with boolean (logical) values. When used with non-Boolean values, it returns `false` if its single operand can be converted to `true`; otherwise, returns `true`.

```!expr
```

## Description

Returns `false` if its single operand can be converted to `true`; otherwise, returns `true`.

If a value can be converted to `true`, the value is so-called truthy. If a value can be converted to `false`, the value is so-called falsy.

Examples of expressions that can be converted to false are:

• `null`;
• `NaN`;
• `0`;
• empty string (`""` or `''` or ````);
• `undefined`.

Even though the `!` operator can be used with operands that are not Boolean values, it can still be considered a boolean operator since its return value can always be converted to a boolean primitive. To explicitly convert its return value (or any expression in general) to the corresponding boolean value, use a double NOT operator (`!!`) or the `Boolean` constructor.

## Examples

### Using NOT

The following code shows examples of the `!` (logical NOT) operator.

```n1 = !true               // !t returns false
n2 = !false              // !f returns true
n3 = !''                 // !f returns true
n4 = !'Cat'              // !t returns false
```

### Double NOT (`!!`)

It is possible to use a couple of NOT operators in series to explicitly force the conversion of any value to the corresponding boolean primitive. The conversion is based on the "truthyness" or "falsyness" of the value (see truthy and falsy).

The same conversion can be done through the `Boolean` function.

```n1 = !!true                   // !!truthy returns true
n2 = !!{}                     // !!truthy returns true: any object is truthy...
n3 = !!(new Boolean(false))   // ...even Boolean objects with a false .valueOf()!
n4 = !!false                  // !!falsy returns false
n5 = !!""                     // !!falsy returns false
n6 = !!Boolean(false)         // !!falsy returns false
```

### Converting between NOTs

The following operation involving booleans:

```!!bCondition
```

is always equal to:

```bCondition
```

## Browser compatibility

Desktop Mobile Server
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet Deno Node.js
`Logical_NOT`
1
12
1
3
3
1
4.4
18
4
10.1
1
1.0
1.0
0.10.0

## See also

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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_NOT