# isNaN

#### Availability

Flash Player 5.

#### Usage

    isNaN(expression)

#### Parameters

`expression` A Boolean, variable, or other expression to be evaluated.

#### Returns

A Boolean value.

#### Description

Top-level function; evaluates the parameter and returns `true` if the value is not a number (`NaN`), indicating the presence of mathematical errors.

#### Example

The following code illustrates return values for the `isNaN` function.

`isNaN("Tree")`

    // returns true

`isNaN(56)`

    // returns false

    isNaN(Number.POSITIVE_INFINITY)
    // returns false

#### See also

`NaN`, `Number.NaN`