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Logical NOT Operator (!) (JavaScript)

Performs logical negation on an expression.

result = !expression

result

Any variable.

expression

Any expression.

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.

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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