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Conditional operator

operator to compare the string and the number without conversion, and of course, a string isn’t equal to

a number, so this outputs

“false”

The not identically equal operator is represented by an exclamation point followed by two equal signs

(

!==

) and returns

true

only if the operands are not equal without conversion. For example:

var sNum = “55”;

var iNum = 55;

alert(sNum != iNum); //outputs “false”

alert(sNum !== iNum); //outputs “true”

Here, the first alert uses the not equal operator, which converts the string

“55”

to the number

, mak-

ing it equal to the second operand, also the number

. Therefore, this evaluates to

false

because the

two are considered equal. The second alert uses the not identically equal operator. It helps to think of

this operation as saying, “is

sNum

different from

iNum

?” The answer to this is yes (

true

), because

sNum

is a string and

iNum

is a number, so they are very different.

Conditional operator

The conditional operator is one of the most versatile in ECMAScript, and it takes on the same form as

in Java:

variable

boolean_expression

true_value

false_value

;

This basically allows a conditional assignment to a variable depending on the evaluation of the

boolean_expression

. If it’s true, then

true_value

is assigned to the variable; if it’s false, then

false_value

is assigned to the variable. For instance:

var iMax = (iNum1 > iNum2) ? iNum1 : iNum2;

In this example,

iMax

is to be assigned the number with the highest value. The expression states that if

iNum1

is greater than

iNum2

iNum1

is assigned to

iMax

. If, however, the expression is false (meaning

that

iNum2

is less than or equal to

iNum1

iNum2

is assigned to

iMax

Assignment operators

Simple assignment is done with the equals sign (

) and simply assigns the value on the right to the vari-

able on the left. For example:

var iNum = 10;

Compound assignment is done with one of the multiplicative, additive, or bitwise shift operators fol-

lowed by an equals sign (=). These assignments are designed as shorthand for such common situations as:

var iNum = 10;

iNum = iNum + 10;

The second line of code can be replaced with a compound assignment:

Chapter 2

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