Logical NOT Operator (!) (JavaScript)

Performs logical negation on an expression.

result = !expression


Any variable.


Any expression.

The following table illustrates how result is determined.

If expression is

Then result is





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.

Supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards. See Version Information.

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