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isNaN Method

Returns a Boolean value that indicates whether a value is the reserved value NaN (not a number).

function isNaN(number : Number) : Boolean

number

Required. A numeric value.

The isNaN function returns true if the value is NaN, and false otherwise. You typically use this function to test return values from the parseInt and parseFloat methods.

Alternatively, a variable that contains NaN or another value could be compared to itself. If it compares as unequal, it is NaN. This is because NaN is the only value that is not equal to itself.

// Returns false.
isNaN(100);
// Returns false.
isNaN("100");
// Returns true.
isNaN("ABC");
// Returns true.
isNaN("10C");
// Returns true.
isNaN(Math.sqrt(-1));

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