# Curly braces in regular expressions in JavaScript

The `'+'`, `'*'`, `'?'` operators are nice, but they cannot be used to specify a certain number of repetitions. In this case, the operator `{}` will come to your aid.

It works as follows: `{5}` - five repetitions, `{2,5}` - repeats from two to five times (both inclusive), `{2,}` - repeats two or more times. Please note that there is no such option - `{,2}`. See examples:

## Example

In this example, the search pattern looks like this: letter `'x'`, letter `'a'` once or twice, letter `'x'`:

`let str = 'xx xax xaax xaaax'; let res = str.replace(/xa{1,2}x/g, '!');`

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

`'xx ! ! xaaax'`

## Example

In this example, the search pattern looks like this: letter `'x'`, letter `'a'` two or more times, letter `'x'`:

`let str = 'xx xax xaax xaaax'; let res = str.replace(/xa{2,}x/g, '!');`

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

`'xx xax ! !'`

## Example

In this example, the search pattern looks like this: letter `'x'`, letter `'a'` three times, letter `'x'`:

`let str = 'xx xax xaax xaaax'; let res = str.replace(/xa{3}x/g, '!');`

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

`'xx xax xaax !'`

## Example

In this example, the search pattern looks like this: letter `'a'` ten times:

`let str = 'aaa aaaaaaaaaa aaa'; let res = str.replace(/a{10}/g, '!');`

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

`'aaa ! aaa'`

## Example

In this example, the code author wanted this pattern: letter `'x'`, letter `'a'` three times or less, letter `'x'`, but, unfortunately, this - {,3} - does not work. It must be specified explicitly:

`let str = 'xx xax xaax xaaax'; let res = str.replace(/xa{1,3}x/g, '!');`

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

`'xx ! ! !'`

## Example

Zero is also allowed:

`let str = 'xx xax xaax xaaax'; let res = str.replace(/xa{0,3}x/g, '!');`

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

`'! ! ! !'`

## Practical tasks

Given a string:

`let str = 'aa aba abba abbba abbbba abbbbba';`

Write a regex that matches only the strings `'abba'`, `'abbba'`, `'abbbba'`.

Given a string:

`let str = 'aa aba abba abbba abbbba abbbbba';`

Write a regex that matches the strings like `'aba'` where `'b'` occurs less than `3` times (inclusive).

Given a string:

`let str = 'aa aba abba abbba abbbba abbbbba';`

Write a regex that matches the strings like `'aba'` where `'b'` occurs more than `4` times (inclusive).

← →
↑
en ru