JavaScript tutorial:
! Operator

The (!) operator is use to perform logical negation on an expression.

Syntax

result = !expression

The ! operator syntax has these parts:

Part	Description
result	Any variable.
expression	Any expression.

Example

The following table illustrates how result is determined.

If expression is	Then result is
True	False
False	True

All unary operators, such as the ! operator, evaluate expressions as follows:

• If applied to undefined or null expressions, a run-time error is raised.

• Objects are converted to strings.

• Strings are converted to numbers if possible. If not, a run-time error is raised.

• Boolean values are treated as numbers (0 if false, 1 if true).

The operator is applied to the resulting number.

For the ! operator, if expression is nonzero, result is zero. If expression is zero, result is 1.