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.
RegExp static properties that expose the last match state globally are deprecated. See deprecated RegExp features for more information.
RegExp.$1, …, RegExp.$9 static accessor properties return parenthesized substring matches.
$9 are static properties of
RegExp, you always use them as
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.
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 |
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