Creating an instance of a regular expression

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.