Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

Chapter 3. Data Types and Values

Computer programs work by manipulating

values
,
such as the number 3.14 or the text "Hello World". The
types of values that can be represented and manipulated in a
programming language are known as

data types ,
and one of the most fundamental characteristics of a programming
language is the set of data types it supports. JavaScript allows you
to work with three


primitive
data types:


numbers, strings of text
(known as "strings"), and boolean truth values (known as
"booleans"). JavaScript also defines two trivial data
types, null and undefined, each of which defines only a single value.

In addition to these primitive data types, JavaScript supports a
composite data type known as


object. An
object (that is, a member of the data type object) represents a
collection of values (either primitive values, like numbers and
strings, or composite values, like other objects). Objects in
JavaScript have a dual nature: an object can represent an unordered
collection of named values or an ordered collection of numbered
values. In the latter case, the object is called an

array
.
Although objects and arrays are fundamentally the same data type in
JavaScript, they behave quite differently and will usually be
considered distinct types throughout this book.

JavaScript defines another special kind of object, known as a

function
.
A function is an object that has executable code associated with it.
A function may be

invoked to perform some kind of operation.
Like arrays, functions behave differently from other kinds of
objects, and JavaScript defines special language syntax for working
with them. Thus, we'll treat the function data type
independently of the object and array types.

In addition to functions and arrays, core JavaScript defines a few
other specialized kinds of objects. These objects do not represent
new data types, just new

classes of objects. The

Date
class defines objects that represent dates, the RegExp class defines
objects that represent regular expressions (a powerful
pattern-matching tool described in
Chapter 10), and the
Error
class defines objects that represent syntax and runtime errors that
can occur in a JavaScript program.

The remainder of this chapter documents each of the primitive data
types in detail. It also introduces the object, array, and function
data types, which are fully documented in Chapter 7,
Chapter 8, and Chapter 9.
Finally, it provides an overview of the Date, RegExp, and Error
classes, which are documented in full detail in the core reference
section of this book.