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Non-standard
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.

Syntax

RegExp.leftContext
RegExp['$`']

Description

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.

Examples

Using leftContext and $`

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

Specifications

Non-standard. Not part of any current specification.

Browser compatibility

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

See also

Метки документа и участники

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