Professional JavaScript For Web Developers

Chapter 2
Just like logical AND, if either operand is not a Boolean, logical OR will not always return a Boolean
value:
❑
❑
❑
❑
❑
If one operand is an object and one is a Boolean, the object is returned.
If both operands are objects, the first operand is returned.
If both operands are null, null is returned.
If either operand is NaN, NaN is returned.
If either operand is undefined, an error occurs.
Also like the logical AND operator, the logical OR operator is short-circuited. In this case, if the first
operand evaluates to true, the second operand is not evaluated. For example:
var bTrue = true;
var bResult = (bTrue || bUnknown);
alert(bResult);
//outputs “true”
As with the previous example, the variable c is undefined. However, because the variable bTrue is set
to true, variable bUnknown is never evaluated and thus the output is “true”. If the value of bTrue is
changed to false, an error occurs:
var bFalse = false;
var bResult = (bTrue || bUnknown); //error occurs here
alert(bResult);
//this line never executes
Multiplicative operators
This next section deals with the three multiplicative operators: multiple, divide, and modulus. These
operators work in a manner similar to their counterparts in languages such as Java, C, and Perl, but they
also include some automatic type conversions you need to be aware of.
Multiply
The multiply operator is represented by an asterisk (*) and is used, as one might suspect, to multiply two
numbers. The syntax is the same as in C:
var iResult = 34 * 56;
However, the multiply operator also has some unique behaviors when dealing with special values:
❑
❑
❑
❑
❑
If the operands are numbers, regular arithmetic multiply is performed, meaning that two positives
or two negatives equal a positive, whereas operands with different signs yield a negative.
If the result is too high or too low, the result is either Infinity or –Infinity.
If either operand is NaN, the result is NaN.
If Infinity is multiplied by 0, the result is NaN.
If Infinity is multiplied by any number other than 0, the result is either Infinity or
–Infinity, depending on the sign of the second operand.
If Infinity is multiplied by Infinity, the result is Infinity.
46