JavaScript Pocket Reference

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JavaScript Pocket Reference

that function. Global variables are visible throughout a Java-

Script program. Variables declared within a function are only

visible within that function. Unlike C, C++, and Java, Java-

Script does not have block-level scope: variables declared

within the curly braces of a compound statement are not

restricted to that block and are visible outside of it.

Data Types

JavaScript supports three primitive data types: numbers,

booleans, and strings; and two compound data types: objects

and arrays. In addition, it defines specialized types of objects

that represent functions, regular expressions, and dates.

Numbers

Numbers in JavaScript are represented in 64-bit floating-

point format. JavaScript makes no distinction between inte-

gers 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 expo-

nent. For example:

1

3.14

0001

6.02e23

Integers may also appear in hexadecimal notation. A hexa-

decimal literal begins with

0x:

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 ...