Javascript - RegExp Constructor Properties

Introduction

The RegExp constructor function has several static properties.

These properties are changed based on the last regular-expression operation performed.

They can be accessed in two different ways:a verbose property name and a shorthand name.

The RegExp constructor properties are listed in the following table.

Verbose Name
Short Name
Description
input
$_
The last string matched against.
lastMatch
$&
The last matched text.
lastParen
$+
The last matched capturing group.
leftContext
$`
The text that appears in the input string prior to lastMatch.
multiline

$*

A Boolean value specifying whether all expressions
should use multiline mode.
rightContext

$'

The text that appears in the input string after
lastMatch.

These properties can extract specific information about the operation performed by exec() or test().

Consider this example:

Demo

var text = "this test is a test test test";
var pattern = /(.)st/g;

if (pattern.test(text)){
    console.log(RegExp.input);//input property contains the original string.
    console.log(RegExp.leftContext);
    console.log(RegExp.rightContext);
    console.log(RegExp.lastMatch);
    console.log(RegExp.lastParen);
    console.log(RegExp.multiline);
}

text = "this test is a test test test";
pattern = /(.)st/g;//from www.j ava  2  s. co  m

if (pattern.test(text)){
    console.log(RegExp.$_);
    console.log(RegExp["$`"]);
    console.log(RegExp["$'"]);
    console.log(RegExp["$&"]);
    console.log(RegExp["$+"]);
    console.log(RegExp["$*"]);
}

Result

Constructor has properties to store up to nine capturing-group matches.

These properties are accessed via RegExp.$1, which contains the first capturing-group match through RegExp.$9, which contains the ninth capturing-group match.

These properties are filled in when calling either exec() or test()

Demo

var text = "this test is a test test test";
var pattern = /(..)or(.)/g;

if (pattern.test(text)){
    console.log(RegExp.$1);/*from   w  ww.  j av  a2  s. com*/
    console.log(RegExp.$2);
    console.log(RegExp.$3);
}

In this example, a pattern with two matching groups is created and tested against a string.

Even though test() simply returns a Boolean value, the properties $1 and $2 are filled in on the RegExp constructor.