RegExp.$1-$9

The non-standard $1, $2, $3, $4, $5, $6, $7, $8, $9 properties are static and read-only properties of regular expressions that contain parenthesized substring matches.

Syntax

RegExp.$1
RegExp.$2
RegExp.$3
RegExp.$4
RegExp.$5
RegExp.$6
RegExp.$7
RegExp.$8
RegExp.$9

Description

The $1, ..., $9 properties are static, they are not a property of an individual regular expression object. Instead, you always use them as RegExp.$1, ..., RegExp.$9.

The values of these properties are read-only and modified whenever successful matches are made.

The number of possible parenthesized substrings is unlimited, but the RegExp object can only hold the last nine. You can access all parenthesized substrings through the returned array's indexes.

These properties can be used in the replacement text for the String.replace method. When used this way, do not prepend them with RegExp. The example below illustrates this. When parentheses are not included in the regular expression, the script interprets $n's literally (where n is a positive integer).

Examples

Using $n with String.replace

The following script uses the replace() method of the String instance to match a name in the format first last and output it in the format last, first. In the replacement text, the script uses $1 and $2 to indicate the results of the corresponding matching parentheses in the regular expression pattern.

var re = /(\w+)\s(\w+)/;
var str = 'John Smith';
str.replace(re, '$2, $1'); // "Smith, John"
RegExp.$1; // "John"
RegExp.$2; // "Smith"

Specifications

Non-standard. Not part of any current specification.

Browser compatibility

See also

• RegExp.input ($_)
• RegExp.lastMatch ($&)
• RegExp.lastParen ($+)
• RegExp.leftContext ($`)
• RegExp.rightContext ($')