Regular Expressions in Node.js

Complete guide to JavaScript Regular Expressions: syntax, patterns, flags, matching, searching, replacing, validation, groups, quantifiers, anchors, character classes, and real-world use cases.

Introduction to Regular Expressions

A regular expression (regex) is a pattern used to match, search, validate, or replace text. Regex is commonly used for input validation, parsing, and text processing.

1. What is a Regular Expression?

Pattern-based string matching.

Creating Regular Expressions

JavaScript provides two ways to create regular expressions.

1. Regex Literal

Use /pattern/flags syntax.

2. RegExp Constructor

Use new RegExp().

Regex Flags

Flags change how regex matches text.

1. Common Flags

i, g, m flags.

Regex Methods

JavaScript provides methods on both RegExp and String for regex operations.

1. test()

Check if pattern matches.

2. match()

Extract matched values.

3. replace()

Replace matched text.

4. search()

Find index of first match.

Character Classes

Character classes allow matching groups of characters.

1. Common Character Classes

Use \d, \w, \s and custom sets.

Quantifiers

Quantifiers specify repetition.

1. Common Quantifiers

* + ? {n,m}

Anchors

Anchors match positions, not characters.

1. ^ and $ Anchors

Match start and end.

Groups & Alternation

Groups allow extracting parts of matches and applying alternation.

1. Capturing Groups

Use parentheses ().

2. Alternation (OR)

Use | operator.

Regex for Validation

Regex is widely used to validate user input.

1. Email Validation (Basic)

Simple email pattern.

2. Numeric String Validation

Check if string contains only digits.