AJAX - The Complete Reference

572 Part IV: Appendixes

We previously covered the type operators used for property access and remind you that

to access a property aProperty of an object object, the following two syntaxes are equivalent:

object.aProperty

object["aProperty"]

Note that the brackets are “real” brackets (they do not imply an optional component).

Comma Operator

The comma operator allows multiple statements to be carried out as one. The syntax of the

operator is

statement1, statement2 [, statement3] ...

The comma is commonly used to separate variables in declarations or parameters in function

calls. However, while uncommon, if this operator is used in an expression, its value is the

value of the last statement.

var x = (4,10,20);

alert(x); // 20

Operator Description Example

delete If the operand is an array element

or object property, the operand is

removed from the array or object.

var myArray = [1,3,5];

delete myArray[1];

alert(myArray);

// shows [1,,5]

instanceof Evaluates true if the first operand

is an instance of the second

operand. The second operand must

be an object (for example,

a constructor).

var today = new Date();

alert(today instanceof Date);

// shows true

in Evaluates true if the first operand

(a string) is the name of a property

of the second operand. The second

operand must be an object (for

example, a constructor).

var robot = {jetpack:true}

alert("jetpack" in robot);

// alerts true

alert("raygun" in robot);

// alerts false

new Creates a new instance of the

object given by the constructor

operand.

var today = new Date();

alert(today);

void Effectively undefines the value of

its expression operand.

var myArray = [1,3,5];

myArray = void myArray;

alert(myArray);

// shows undefined

TABLE A-16 Type-Related Operators