There are two ways to create
a regular expression instance. One way uses forward slash characters
(
/
) to delineate the regular expression; the other
uses the
new
constructor. For example, the following
regular expressions are equivalent:
var pattern1:RegExp = /bob/i;
var pattern2:RegExp = new RegExp("bob", "i");
Forward slashes delineate a regular expression literal in the
same way as quotation marks delineate a string literal. The part
of the regular expression within the forward slashes defines the
pattern.
The
regular expression can also include
flags
after the final
delineating slash. These flags are considered to be part of the
regular expression, but they are separate from its pattern.
When using the
new
constructor, you use two
strings to define the regular expression. The first string defines
the pattern, and the second string defines the flags, as in the
following example:
var pattern2:RegExp = new RegExp("bob", "i");
When including a forward slash
within
a regular expression
that is defined by using the forward slash delineators, you must
precede the forward slash with the backslash (
\
)
escape character. For example, the following regular expression matches
the pattern
1/2
:
var pattern:RegExp = /1\/2/;
To include quotation marks
within
a regular expression
that is defined with the
new
constructor, you must
add backslash (
\
) escape character before the quotation
marks (just as you would when defining any String literal). For example,
the following regular expressions match the pattern
eat at "joe's"
:
var pattern1:RegExp = new RegExp("eat at \"joe's\"", "");
var pattern2:RegExp = new RegExp('eat at "joe\'s"', "");
Do not use the backslash escape character with quotation marks
in regular expressions that are defined by using the forward slash
delineators. Similarly, do not use the escape character with forward
slashes in regular expressions that are defined with the
new
constructor.
The following regular expressions are equivalent, and they define
the pattern
1/2 "joe's"
:
var pattern1:RegExp = /1\/2 "joe's"/;
var pattern2:RegExp = new RegExp("1/2 \"joe's\"", "");
var pattern3:RegExp = new RegExp('1/2 "joe\'s"', '');
Also, in a regular expression that is defined with the
new
constructor,
to use a metasequence that begins with the backslash (
\
)
character, such as
\d
(which matches any digit),
type the backslash character twice:
var pattern:RegExp = new RegExp("\\d+", ""); // matches one or more digits
You must type the backlash character twice in this case, because
the first parameter of the
RegExp()
constructor
method is a string, and in a string literal you must type a backslash
character twice to have it recognized as a single backslash character.
The sections that follow describe syntax for defining regular
expression patterns.
For more information on flags, see
Flags and properties
.
