! (Logical NOT) : Boolean Operators « Operators « JavaScript Tutorial






  1. JavaScript Tutorial
  2. Operators
  3. Boolean Operators

The logical NOT operator is indicated by an exclamation point (!).

The logical NOT always returns a Boolean value.

The logical NOT operator behaves in the following way:

  1. If the operand is an object, false is returned.
  2. If the operand is the number 0, true is returned.
  3. If the operand is any number other than 0, false is returned.
  4. If the operand is null, true is returned.
  5. If the operand is NaN, true is returned.
  6. If the operand is undefined, an error occurs.
<html>
    <script language="JavaScript">
    <!--
    theTruth = new String("1");
    theReverseTruth = !theTruth;
    document.write("theTruth = ",theTruth,"<br>");
    document.write("theReverseTruth = ",theReverseTruth);
    -->
    </script>
</html>








2.6.Boolean Operators
2.6.1.JavaScript provides three Boolean operators
2.6.2.Logical AND
2.6.3.! (Logical NOT)
2.6.4.Use logical NOT to control the loop
2.6.5.|| (Logical OR)