2. [Regular Expressions:](./docs/regular-expressions.md)

- [Creating regular expressions](./docs/regular-expressions.md#-creating-regular-expressions)

- [Common regular expression patterns](./docs/regular-expressions.md#-common-regular-expression-patterns)

- [Matching patterns in strings](./docs/regular-expressions.md#-matching-patterns-in-strings)

A regular expression, often abbreviated as `regex`. It is a sequence of characters that defines a search pattern. It's used to match, find, replace, or manipulate text based on given patterns.

1. [Creating regular expressions](#-creating-regular-expressions)

2. [Common regular expression patterns](#-common-regular-expression-patterns)

3. [Matching patterns in strings](#-matching-patterns-in-strings)

Regular expressions can be created in two ways:

- Literal notation:

```javascript

let pattern = /pattern/;

```

- Constructor:

```javascript

let pattern = new RegExp("pattern");

```

**Flags:**

Regular expressions can have flags that modify their behavior:

- `i`: Case-insensitive matching.

- `g`: Global matching, finding all matches instead of just the first.

- `m`: Multiline matching, allowing `^` and `$` to match the beginning and end of lines, respectively.

- `.`: Matches any character except a newline.

- `^`: Matches the beginning of a string or line.

- `$`: Matches the end of a string or line.

- `*`: Matches zero or more occurrences of the preceding character or group.

- `+`: Matches one or more occurrences of the preceding character or group.

- `?`: Matches zero or one occurrence of the preceding character or group.  

- `{n}`: Matches exactly n occurrences of the preceding character or group.

- `{n,}`: Matches at least n occurrences of the preceding character or group.  

- `{n,m}`: Matches between n and m occurrences of the preceding character or group.  

- `|`: Matches either the expression before or after it.

- `()`: Groups a part of the regular expression.

- `[ ]`: Matches any character within the brackets.

- `[^ ]`: Matches any character not within the brackets

let text = "The quick brown fox jumps over the lazy dog.";

let pattern = /fox/;

let match = text.match(pattern);

console.log(match); // Output: ["fox"]

let index = text.search(pattern);

console.log(index); // Output: 16

let replacedText = text.replace(pattern, "cat");

console.log(replacedText); // Output: "The quick brown cat jumps over the lazy dog."

**Other Methods:**

There are several methods to work with regular expressions:

- `match()`: Finds all matches of a regular expression in a string and returns an array.

- `search()`: Finds the index of the first match of a regular expression in a string.

- `replace()`: Replaces all matches of a regular expression in a string with a new string.

- `test()`: Checks if a string matches a regular expression and returns a boolean.

- `split()`: Splits a string into an array using a regular expression as a separator.

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