RegExp.leftContext ($`)

This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

The non-standard leftContext property is a static and read-only property of regular expressions that contains the substring preceding the most recent match. RegExp.$` is an alias for this property.




The leftContext property is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.leftContext or RegExp['$`'].

The value of the leftContext property is read-only and modified whenever a successful match is made.

You can not use the shorthand alias with the dot property accessor (RegExp.$`), because the parser expects a starting template string in that case and a SyntaxError is thrown. Use the bracket notation for property access.


Using leftContext and $`

var re = /world/g;
re.test("hello world!");
RegExp.leftContext; // "hello "
RegExp['$`'];       // "hello "


Non-standard. Not part of any current specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

JavaScript Property Read-only Reference RegExp Regular Expressions