# Default capturing groups in the replace method in JavaScript regexes

In the replace method, in addition to capturing groups with your numbers, standard capturing groups are always available: `$&` - entire match found, `$`` and `$'` - part of a string before and after the match. Let's see how they work with examples.

## Example

Let's find all the numbers and enclose them in parentheses:

`let str = '1 23 456'; let res = str.replace(/\d+/g, '($&)');`

As a result, the following will be written to the variable:

`'(1) (23) (456)'`

## Example

Let's find the @ symbol and replace it with a content before it, @ symbol, and a content after it. We write all this in parentheses:

`let str = '123@456'; let res = str.replace(/@/g, "($`@$')");`

As a result, the following will be written to the variable:

`'123(123@456)456'`

## Example

Let's say we want to find a dollar symbol and wrap it in quotes ````. In this case, in order for `$`` not to be interpreted as a command, the dollar sign must be doubled:

`let str = 'aaa $ bbb'; let res = str.replace(/\$/g, '`$$`');`

As a result, the following will be written to the variable:

`'aaa `$` bbb'`

## Practical tasks

Given a string:

`let str = 'a1b2c3';`

Write a regex that next to each digit will write the same one.

Given a string:

`let str = 'sss site.ru zzz site.com kkk';`

Replace domains with links like:

`<a href="http://site.ru">site.ru</a>`
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