| 2. 6. 1. JavaScript provides three Boolean operators |
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JavaScript defines true as anything other than 0 (zero), "" (empty string), null, undefined, and false. |
Logical AND (&& ) |
The logical AND operator (&&) returns true if the expression to the both sides of the operator evaluates to true. |
If either the left, right, or both expressions evaluate to false, the result of the operation is false. |
The AND operation begins by evaluating the left operand. |
If the left operand evaluates false, the basic logic of the AND operator is complete. |
But if the left operand evaluates true, the right operand must be evaluated. |
Logical OR |
The logical OR operator (||) returns false if the expression to the both sides of the operator evaluates to false. |
If one of the left and the right expressions evaluate to true, the result of the operation is true. |
The OR operation begins by evaluating the left operand. |
If the left operand evaluates true, the basic logic of the OR operator is complete. |
But if the left operand evaluates false, the right operand must be evaluated. |
Logical NOT |
If the expression evaluates to true, the result of the logical NOT operator (!) is false. |
If the expression evaluates to false, the result is true. |
When the expression evaluates to a non-Boolean value, it is converted to true or false before performing the inversion. |
Identity |
If the value on the left is equal to the value on the right side of the operator, true is returned from the identity operator (===). |
If the values are not equal, false is returned. |
No type-conversion is performed on the operands before the comparison. |
Non-Identity |
If the value on the left is not equal to the value on the right side of the operator, true is returned from the non-identity operator (!==). |
If the values are equal, false is returned. |
No type-conversion is performed on the operands before the comparison is made. |
The identity and non-identity operators are only available in JavaScript 1.3 and later. |
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<html>
<script language="JavaScript">
<!--
x = 3;
if((2==x) && (x=5)) {
document.write("The && evaluated TRUE!<br>");
}
else
{
document.write("The && evaluated FALSE!<br>");
}
document.write("x=",x,"<br>");
-->
</script>
</html>
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