Js Regex — Free Javascript Tutorial

TL;DR: Learn Js Regex in Javascript with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Js Regex in Javascript

Regular Expressions (regex) are patterns used to match, search, and manipulate text. In JavaScript, regex literals are written between forward slashes: /pattern/flags.

Core syntax: . (any character), * (0 or more), + (1 or more), ? (0 or 1), ^ (start), $ (end), [abc] (character class), [^abc] (not), \d (digit), \w (word char), \s (whitespace), {n,m} (repeat n to m times).

Flags: g (global — find all matches), i (case-insensitive), m (multiline). Methods: test() (returns boolean), match() (returns array), replace() (substitute), split() (divide by pattern), exec() (iterative matching).

Common use cases: form validation (email, phone, password), data extraction (find all URLs in text), text formatting (add spaces to phone numbers), sanitisation (remove HTML tags).

// Create regex:
const re = /pattern/flags;     // literal
const re = new RegExp("pat");  // constructor

// Test:
/\d+/.test("abc123")    // → true

// Match:
"hello".match(/[aeiou]/g)   // → ['e', 'o']

// Replace:
"a1b2".replace(/\d/g, '#') // → "a#b#"

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