JavaScript Pocket Reference

The JavaScript Language

|

9

the keyword this refers to the object for which the function

is a property.

Within the body of a function, the

arguments[] array con-

tains the complete set of arguments passed to the function.

See Function and Arguments in the reference section.

null and undefined

There are two JavaScript values that are not of any of the

types described above. The JavaScript keyword

null is a spe-

cial value that indicates “no value”. If a variable contains

null, you know that it does not contain a valid value of any

other type. The other special value in JavaScript is the unde-

fined value. This is the value of uninitialized variables and

the value returned when you query object properties that do

not exist. In JavaScript 1.5, there is a pre-defined global vari-

able named

undefined that holds this special undefined

value.

null and undefined serve similar purposes and the ==

operator considers them equal; if you need to distinguish

between them, use the

=== operator.

Expressions and Operators

JavaScript expressions are formed by combining values

(which may be literals, variables, object properties, array ele-

ments, or function invocations) using JavaScript operators.

Parentheses can be used in an expression to group subex-

pressions and alter the default order of evaluation of the

expression. Some examples:

1+2

total/n

sum(o.x, a[3])++

JavaScript defines a complete set of operators, most of which