RegExp.$1, …, RegExp.$9

Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

Note: All RegExp static properties that expose the last match state globally are deprecated. See deprecated RegExp features for more information.

The RegExp.$1, …, RegExp.$9 static accessor properties return parenthesized substring matches.


Because $1$9 are static properties of RegExp, you always use them as RegExp.$1, RegExp.$2, etc., rather than as properties of a RegExp object you created.

The values of $1, …, $9 update whenever a RegExp (but not a RegExp subclass) instance makes a successful match. If no matches have been made, or if the last match does not have the corresponding capturing group, the respective property is an empty string. The set accessor of each property is undefined, so you cannot change the properties directly.

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

$1, …, $9 can also be used in the replacement string of String.prototype.replace(), but that's unrelated to the RegExp.$n legacy properties.


Using $n with RegExp.prototype.test()

The following script uses the test() method of the RegExp instance to grab a number in a generic string.

const str = "Test 24";
const number = /(\d+)/.test(str) ? RegExp.$1 : "0";
number; // "24"

Please note that any operation involving the usage of other regular expressions between a re.test(str) call and the RegExp.$n property, might have side effects, so that accessing these special properties should be done instantly, otherwise the result might be unexpected.


Legacy RegExp features
# additional-properties-of-the-regexp-constructor

Browser compatibility

BCD tables only load in the browser

See also