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.leftContext static accessor property returns the substring preceding the most recent match.
RegExp["$`"] is an alias for this property.
leftContext is a static property of
RegExp, you always use it as
RegExp["$`"], rather than as a property of a
RegExp object you created.
The value of
leftContext updates whenever a
RegExp (but not a
RegExp subclass) instance makes a successful match. If no matches have been made,
leftContext is an empty string. The set accessor of
undefined, so you cannot change this property directly.
$` can also be used in the replacement string of
String.prototype.replace(), but that's unrelated to the
RegExp["$`"] legacy property.
const re = /world/g; re.test("hello world!"); RegExp.leftContext; // "hello " RegExp["$`"]; // "hello "
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