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

2.7 Identifiers

An

identifier is simply a name. In JavaScript,
identifiers are used to name


variables
and functions and to provide labels for certain loops in JavaScript
code. The rules for legal identifier names are the same in JavaScript
as they are in Java and many other languages. The first character
must be a
letter, an underscore
(_), or a dollar sign
($).[1] Subsequent characters may be any letter or digit or an
underscore or dollar sign. (Numbers are not allowed as the first
character so that JavaScript can easily distinguish identifiers from
numbers.) These are all legal
identifiers:

In ECMAScript v3, identifiers can
contain letters and digits from the complete Unicode character set.
Prior to this version of the standard, JavaScript identifiers are
restricted to the ASCII character set. ECMAScript v3 also allows
Unicode escape sequences to appear in identifiers. A Unicode escape
is the characters \u followed by 4 hexadecimal
digits that specify a 16-bit character encoding. For example, the
identifier could also be written as \u03c0.
Although this is an awkward syntax, it makes it possible to translate
JavaScript programs that contain Unicode characters into a form that
allows them to be manipulated with text editors and other tools that
do not support the full Unicode character set.

Finally, identifiers cannot be the same as any of the
keywords used for other purposes in
JavaScript. The next section lists the special names that are
reserved in JavaScript.