Webmaster in a Nutshell, Second Edition

Data Types

JavaScript supports three primitive data types: numbers, boolean values, and strings. In addition, it supports two compound data types: object and arrays. Functions are also a first-class data type in JavaScript, and JavaScript 1.2 adds support for regular expressions (described later) as a specialized type of object.

Numbers

Numbers in JavaScript are represented in 64-bit floating-point format. JavaScript makes no distinction between integers and floating-point numbers. Numeric literals appear in JavaScript programs using the usual syntax: a sequence of digits, with an optional decimal point and an optional exponent. For example:

1
3.14
.0001
6.02e23

Integers may also appear in octal or hexadecimal notation. An octal literal begins with 0, and a hexadecimal literal begins with 0x:

0377 // The number 255 in octal
0xFF // The number 255 in hexadecimal

When a numeric operation overflows, it returns a special value that represents positive or negative infinity. When an operation underflows, it returns zero. When an operation such as taking the square root of a negative number yields an error or meaningless result, it returns the special value NaN, which represents a value that is not-a-number. Use the global function isNaN() to test for this value. The Number object defines useful numeric constants. The Math object defines various mathematical operations.

Booleans

The boolean type has two possible values, represented by the JavaScript keywords true and false. These values represent ...