JavaScript Regular Expressions Mastery: Real-World Patterns & Validation
Master regex with real-world patterns — email validation, URL parsing, log extraction, password enforcement, and more. Covers groups, lookaheads, Unicode, and performance tips.
Feb 16, 202625 min read
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JavaScript MasteryPart 11 of 11
- 1. JavaScript Type Coercion Mastery: A Senior Engineer's Guide to the Chaos
- 2. JavaScript Runtime Deep Dive: Event Loop, Call Stack & Async Execution
- 3. Mastering JavaScript Callbacks: From Sync to Async & The Event Loop
- 4. JavaScript Closures Deep Dive: Mastering Lexical Scope & Memory
- 5. JavaScript Object Prototyping Mastery: A Visual Guide to Inheritance
- 6. Demystifying the JavaScript 'this' Keyword: A Visual Guide
- 7. JavaScript Promises & Promise Chaining Mastery: From Callbacks to Async Flow
- 8. JavaScript Array Methods Mastery: Complete Guide from map() to reduce()
- 9. JavaScript Map & Set Mastery: Complete Guide to Modern Data Structures
- 10. JavaScript String Methods Mastery: Complete Guide from slice() to replaceAll()
- 11. JavaScript Regular Expressions Mastery: Real-World Patterns & Validation
Introduction
Regular expressions (regex) are one of the most powerful tools in a developer's arsenal—and one of the most misunderstood. They let you search, validate, extract, and transform text with surgical precision. Yet many developers avoid them, copy-pasting patterns from Stack Overflow without truly understanding them.
This guide takes a different approach. Instead of dry theory, every pattern is tied to a real-world use case you'll actually encounter—email validation, URL parsing, log file analysis, password strength checking, and more. By the end, you'll read and write regex with confidence.
ℹ️ note[!NOTE] JavaScript regex uses the
RegExpobject. You can create patterns using literal syntax/pattern/flagsor the constructornew RegExp('pattern', 'flags').
The Regex Toolkit: Methods at a Glance
| Method | Returns | Use Case |
|---|---|---|
str.match(regex) | Array of matches or null | Find all occurrences |
str.matchAll(regex) | Iterator of detailed matches | Find with capture groups |
str.search(regex) | Index or -1 | Find position of first match |
str.replace(regex, rep) | New string | Replace matches |
str.replaceAll(regex, rep) | New string | Replace all matches |
str.split(regex) | Array | Split by pattern |
regex.test(str) | boolean | Test if pattern matches |
regex.exec(str) | Match array or null | Detailed single match |
1. Regex Fundamentals
1.1 Creating Regular Expressions
javascript
// Literal syntax (preferred for static patterns)
const regex1 = /hello/i;
// Constructor syntax (for dynamic patterns)
const searchTerm = 'hello';
const regex2 = new RegExp(searchTerm, 'i');
// When to use constructor: pattern is built from variables
function findWord(text, word) {
const regex = new RegExp(`\\b${word}\\b`, 'gi');
return text.match(regex);
}
findWord('Hello world, hello there!', 'hello');
// ['Hello', 'hello']
⚠️ warning[!WARNING] When using
new RegExp(), you must double-escape special characters:\\dinstead of\d,\\binstead of\b.
1.2 Flags
| Flag | Name | Effect |
|---|---|---|
g | Global | Find all matches, not just the first |
i | Case-insensitive | A matches a |
m | Multiline | ^ and $ match line boundaries |
s | DotAll | . matches newlines too |
u | Unicode | Correct handling of Unicode characters |
d | Has indices | Provides start/end indices for captures |
v | UnicodeSets | Extended Unicode property support (ES2024) |
javascript
// Combining flags
const regex = /pattern/gim;
2. Character Classes & Quantifiers
2.1 Built-in Character Classes
| Pattern | Meaning | Equivalent | Real-World Use |
|---|---|---|---|
\d | Any digit | [0-9] | Phone numbers, ZIP codes |
\D | Non-digit | [^0-9] | Strip numbers from text |
\w | Word character | [a-zA-Z0-9_] | Usernames, identifiers |
\W | Non-word character | [^a-zA-Z0-9_] | Find special characters |
\s | Whitespace | [ \t\n\r\f\v] | Trim, normalize spaces |
\S | Non-whitespace | [^ \t\n\r\f\v] | Extract tokens |
. | Any character (except newline) | Wildcard matching | |
\b | Word boundary | Whole word search |
2.2 Quantifiers
| Quantifier | Meaning | Example | Matches |
|---|---|---|---|
* | 0 or more | \d* | '', '5', '123' |
+ | 1 or more | \d+ | '5', '123' (not '') |
? | 0 or 1 | colou?r | 'color', 'colour' |
{n} | Exactly n | \d{4} | '2026' |
{n,} | n or more | \d{2,} | '12', '123', '1234' |
{n,m} | Between n and m | \d{2,4} | '12', '123', '1234' |
2.3 Greedy vs Lazy
javascript
const html = '<div>Hello</div><div>World</div>';
// Greedy (default) — matches as MUCH as possible
html.match(/<div>.*<\/div>/);
// ['<div>Hello</div><div>World</div>'] — grabs everything!
// Lazy (add ?) — matches as LITTLE as possible
html.match(/<div>.*?<\/div>/g);
// ['<div>Hello</div>', '<div>World</div>'] — each tag separately
💜 important[!IMPORTANT] Use lazy quantifiers (
*?,+?,??) when parsing structured text like HTML, JSON, or log files to avoid over-matching.
3. Real-World Validation Patterns
3.1 Email Validation
javascript
function isValidEmail(email) {
// RFC 5322 simplified — covers 99% of real emails
const regex = /^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/;
return regex.test(email);
}
console.log(isValidEmail('user@example.com')); // true
console.log(isValidEmail('john.doe+tag@gmail.com')); // true
console.log(isValidEmail('invalid@')); // false
console.log(isValidEmail('@nodomain.com')); // false
console.log(isValidEmail('spaces here@mail.com')); // false
Breaking it down:
| Part | Meaning |
|---|---|
^[a-zA-Z0-9.!#$%&'*+/=?^_{ | }~-]+` |
@ | Literal @ symbol |
[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])? | Domain label: starts and ends with alphanumeric |
(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$ | Additional domain labels separated by dots |
3.2 Password Strength Validation
javascript
function validatePassword(password) {
const checks = {
length: password.length >= 8,
uppercase: /[A-Z]/.test(password),
lowercase: /[a-z]/.test(password),
digit: /\d/.test(password),
special: /[!@#$%^&*()_+\-=\[\]{};':"\\|,.<>\/?]/.test(password),
};
const strength = Object.values(checks).filter(Boolean).length;
return {
checks,
strength,
label: strength <= 2 ? 'Weak' : strength <= 4 ? 'Medium' : 'Strong'
};
}
console.log(validatePassword('hello'));
// { checks: { length: false, ... }, strength: 1, label: 'Weak' }
console.log(validatePassword('MyP@ssw0rd!'));
// { checks: { length: true, ... }, strength: 5, label: 'Strong' }
3.3 Phone Number Validation (International)
javascript
function validatePhone(phone) {
// Supports: +1-234-567-8900, (234) 567-8900, 234.567.8900, +91 98765 43210
const regex = /^(\+?\d{1,3}[-.\s]?)?\(?\d{1,4}\)?[-.\s]?\d{1,4}[-.\s]?\d{1,9}$/;
return regex.test(phone.trim());
}
console.log(validatePhone('+1-234-567-8900')); // true
console.log(validatePhone('(234) 567-8900')); // true
console.log(validatePhone('+91 98765 43210')); // true
console.log(validatePhone('234.567.8900')); // true
console.log(validatePhone('abc')); // false
3.4 URL Validation & Parsing
javascript
function parseURL(url) {
const regex = /^(https?):\/\/([^\/\s:]+)(?::(\d+))?(\/[^\s?#]*)?(?:\?([^\s#]*))?(?:#(\S*))?$/;
const match = url.match(regex);
if (!match) return null;
return {
protocol: match[1],
hostname: match[2],
port: match[3] || null,
pathname: match[4] || '/',
query: match[5] || null,
hash: match[6] || null
};
}
console.log(parseURL('https://api.example.com:8080/users?page=1&limit=10#section'));
// {
// protocol: 'https',
// hostname: 'api.example.com',
// port: '8080',
// pathname: '/users',
// query: 'page=1&limit=10',
// hash: 'section'
// }
3.5 Credit Card Number Validation
javascript
function detectCardType(number) {
const cleaned = number.replace(/\s|-/g, '');
const patterns = {
visa: /^4\d{12}(?:\d{3})?$/,
mastercard: /^5[1-5]\d{14}$/,
amex: /^3[47]\d{13}$/,
discover: /^6(?:011|5\d{2})\d{12}$/,
};
for (const [type, regex] of Object.entries(patterns)) {
if (regex.test(cleaned)) return type;
}
return 'unknown';
}
console.log(detectCardType('4532 0151 1283 0366')); // 'visa'
console.log(detectCardType('5425 2334 3010 9903')); // 'mastercard'
console.log(detectCardType('3782 822463 10005')); // 'amex'
4. Groups and Captures
4.1 Capturing Groups ()
javascript
// Extract date parts from ISO format
const dateStr = '2026-02-12T15:30:00Z';
const match = dateStr.match(/(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2})/);
const [full, year, month, day, hour, minute, second] = match;
console.log({ year, month, day, hour, minute, second });
// { year: '2026', month: '02', day: '12', hour: '15', minute: '30', second: '00' }
4.2 Named Groups (?<name>)
Named groups make patterns self-documenting:
javascript
// Parse a git commit line
const commitLine = 'abc1234 John Doe <john@example.com> 2026-02-12 Fix login bug';
const regex = /^(?<hash>[a-f0-9]+)\s+(?<author>[^<]+)<(?<email>[^>]+)>\s+(?<date>\d{4}-\d{2}-\d{2})\s+(?<message>.+)$/;
const { groups } = commitLine.match(regex);
console.log(groups);
// {
// hash: 'abc1234',
// author: 'John Doe ',
// email: 'john@example.com',
// date: '2026-02-12',
// message: 'Fix login bug'
// }
4.3 Non-Capturing Groups (?:)
When you need grouping but don't want to capture:
javascript
// Match file extensions without capturing the dot group
const filename = 'report.pdf';
// ❌ Captures unnecessary group
const match1 = filename.match(/\.(\w+)$/);
console.log(match1[1]); // 'pdf' (but index 0 is '.pdf')
// ✅ Using non-capturing group for alternatives
const isImage = /\.(?:jpg|jpeg|png|gif|webp|svg)$/i.test('photo.JPG');
console.log(isImage); // true
4.4 Backreferences
Reference previously captured groups within the same pattern:
javascript
// Find repeated words (common typo)
const text = 'The the quick brown fox fox jumped';
const regex = /\b(\w+)\s+\1\b/gi;
const matches = text.match(regex);
console.log(matches); // ['The the', 'fox fox']
// Fix duplicate words
const fixed = text.replace(/\b(\w+)\s+\1\b/gi, '$1');
console.log(fixed); // 'The quick brown fox jumped'
javascript
// Validate matching HTML tags
function hasMatchingTags(html) {
return /<(\w+)[^>]*>.*?<\/\1>/s.test(html);
}
console.log(hasMatchingTags('<div>Hello</div>')); // true
console.log(hasMatchingTags('<div>Hello</span>')); // false
5. Lookahead & Lookbehind (Zero-Width Assertions)
These assert that a pattern exists (or doesn't) without consuming characters.
| Assertion | Syntax | Meaning |
|---|---|---|
| Positive Lookahead | (?=...) | Must be followed by |
| Negative Lookahead | (?!...) | Must NOT be followed by |
| Positive Lookbehind | (?<=...) | Must be preceded by |
| Negative Lookbehind | (?<!...) | Must NOT be preceded by |
5.1 Password Enforcement with Lookaheads
javascript
// Password must have: 8+ chars, uppercase, lowercase, digit, special
function isStrongPassword(password) {
const regex = /^(?=.*[A-Z])(?=.*[a-z])(?=.*\d)(?=.*[!@#$%^&*]).{8,}$/;
return regex.test(password);
}
console.log(isStrongPassword('MyP@ss1')); // false (too short)
console.log(isStrongPassword('MyP@ssw0rd')); // true
console.log(isStrongPassword('mypassword1')); // false (no uppercase, no special)
5.2 Format Currency Without Capturing
javascript
// Add commas to numbers: 1234567 → 1,234,567
function formatNumber(num) {
return num.toString().replace(
/\B(?=(\d{3})+(?!\d))/g,
','
);
}
console.log(formatNumber(1234567)); // '1,234,567'
console.log(formatNumber(1000000000)); // '1,000,000,000'
console.log(formatNumber(42)); // '42'
How it works:
\B— non-word boundary (not at start)(?=(\d{3})+(?!\d))— lookahead: followed by groups of 3 digits, then no more digits
5.3 Extract Prices Without Currency Symbol
javascript
// Get price values from text, excluding the $ symbol
const text = 'Laptop: $999.99, Mouse: $29.50, Keyboard: $79.00';
const prices = [...text.matchAll(/(?<=\$)\d+(?:\.\d{2})?/g)]
.map(m => parseFloat(m[0]));
console.log(prices); // [999.99, 29.5, 79]
5.4 Find Words NOT Preceded by a Pattern
javascript
// Find "script" that's NOT part of "JavaScript"
const text = 'JavaScript uses script tags. TypeScript also has scripts.';
const matches = [...text.matchAll(/(?<!Java|Type)script/gi)]
.map(m => ({ match: m[0], index: m.index }));
console.log(matches);
// [{ match: 'script', index: 21 }] — only the standalone "script"
6. Real-World Data Extraction
6.1 Parse Log Files
javascript
const logLine = '2026-02-12 15:30:42 [ERROR] UserService: Failed to authenticate user_id=12345 ip=192.168.1.100';
const logRegex = /^(?<timestamp>\d{4}-\d{2}-\d{2}\s\d{2}:\d{2}:\d{2})\s\[(?<level>\w+)\]\s(?<service>\w+):\s(?<message>.+)$/;
const { groups } = logLine.match(logRegex);
console.log(groups);
// {
// timestamp: '2026-02-12 15:30:42',
// level: 'ERROR',
// service: 'UserService',
// message: 'Failed to authenticate user_id=12345 ip=192.168.1.100'
// }
// Extract key=value pairs from the message
const kvPairs = {};
for (const match of groups.message.matchAll(/(\w+)=([\w.]+)/g)) {
kvPairs[match[1]] = match[2];
}
console.log(kvPairs); // { user_id: '12345', ip: '192.168.1.100' }
6.2 Parse CSV with Quoted Fields
javascript
function parseCSVLine(line) {
const regex = /(?:^|,)("(?:[^"]|"")*"|[^,]*)/g;
const fields = [];
for (const match of line.matchAll(regex)) {
let value = match[1];
// Remove surrounding quotes and unescape doubled quotes
if (value.startsWith('"') && value.endsWith('"')) {
value = value.slice(1, -1).replace(/""/g, '"');
}
fields.push(value);
}
return fields;
}
const csvLine = 'John,"Doe, Jr.",30,"He said ""hello"""';
console.log(parseCSVLine(csvLine));
// ['John', 'Doe, Jr.', '30', 'He said "hello"']
6.3 Extract Markdown Links
javascript
function extractLinks(markdown) {
const regex = /\[(?<text>[^\]]+)\]\((?<url>[^)]+)\)/g;
const links = [];
for (const match of markdown.matchAll(regex)) {
links.push({
text: match.groups.text,
url: match.groups.url
});
}
return links;
}
const md = `
Check out [Google](https://google.com) and
[MDN Web Docs](https://developer.mozilla.org) for references.
Also see [my blog](/blog/javascript-regex).
`;
console.log(extractLinks(md));
// [
// { text: 'Google', url: 'https://google.com' },
// { text: 'MDN Web Docs', url: 'https://developer.mozilla.org' },
// { text: 'my blog', url: '/blog/javascript-regex' }
// ]
6.4 Sanitize & Transform User Input
javascript
// Remove HTML tags (basic sanitizer)
function stripHTML(html) {
return html.replace(/<[^>]*>/g, '');
}
console.log(stripHTML('<p>Hello <strong>World</strong></p>'));
// 'Hello World'
// Convert camelCase to kebab-case
function camelToKebab(str) {
return str.replace(/([a-z0-9])([A-Z])/g, '$1-$2').toLowerCase();
}
console.log(camelToKebab('backgroundColor')); // 'background-color'
console.log(camelToKebab('borderTopWidth')); // 'border-top-width'
console.log(camelToKebab('fontSize')); // 'font-size'
// Convert kebab-case to camelCase
function kebabToCamel(str) {
return str.replace(/-([a-z])/g, (_, letter) => letter.toUpperCase());
}
console.log(kebabToCamel('background-color')); // 'backgroundColor'
console.log(kebabToCamel('border-top-width')); // 'borderTopWidth'
6.5 Parse Environment Variables
javascript
function parseEnvFile(content) {
const regex = /^(?<key>[A-Z_][A-Z0-9_]*)=(?<value>"[^"]*"|'[^']*'|[^\s#]+)/gm;
const env = {};
for (const match of content.matchAll(regex)) {
let value = match.groups.value;
// Strip surrounding quotes
if ((value.startsWith('"') && value.endsWith('"')) ||
(value.startsWith("'") && value.endsWith("'"))) {
value = value.slice(1, -1);
}
env[match.groups.key] = value;
}
return env;
}
const envFile = `
DATABASE_URL="postgres://localhost:5432/mydb"
API_KEY=sk-abc123def456
PORT=3000
# This is a comment
NODE_ENV='production'
`;
console.log(parseEnvFile(envFile));
// {
// DATABASE_URL: 'postgres://localhost:5432/mydb',
// API_KEY: 'sk-abc123def456',
// PORT: '3000',
// NODE_ENV: 'production'
// }
7. Search & Replace Patterns
7.1 Replace with Functions
javascript
// Censor bad words
function censor(text, badWords) {
const regex = new RegExp(`\\b(${badWords.join('|')})\\b`, 'gi');
return text.replace(regex, match => '*'.repeat(match.length));
}
console.log(censor('This is damn bad!', ['damn', 'bad']));
// 'This is **** ***!'
7.2 Template Engine
javascript
function renderTemplate(template, data) {
return template.replace(
/\{\{(\w+)\}\}/g,
(match, key) => data[key] !== undefined ? data[key] : match
);
}
const template = 'Hello {{name}}, welcome to {{company}}! Your role is {{role}}.';
const result = renderTemplate(template, {
name: 'Alice',
company: 'TechCorp'
});
console.log(result);
// 'Hello Alice, welcome to TechCorp! Your role is {{role}}.'
7.3 Smart Slug Generator
javascript
function slugify(text) {
return text
.normalize('NFD') // Decompose accents
.replace(/[\u0300-\u036f]/g, '') // Remove accent marks
.toLowerCase()
.replace(/[^a-z0-9\s-]/g, '') // Remove special characters
.replace(/\s+/g, '-') // Spaces to hyphens
.replace(/-+/g, '-') // Collapse multiple hyphens
.replace(/^-|-$/g, ''); // Trim leading/trailing hyphens
}
console.log(slugify('Héllo Wörld! @2026')); // 'hello-world-2026'
console.log(slugify('JavaScript & TypeScript: A Guide'));
// 'javascript--typescript-a-guide' → 'javascript-typescript-a-guide'
7.4 Syntax Highlighter (Simplified)
javascript
function highlightJS(code) {
const rules = [
{ regex: /(\/\/.*$)/gm, class: 'comment' },
{ regex: /("(?:[^"\\]|\\.)*"|'(?:[^'\\]|\\.)*'|`(?:[^`\\]|\\.)*`)/g, class: 'string' },
{ regex: /\b(\d+(?:\.\d+)?)\b/g, class: 'number' },
{ regex: /\b(const|let|var|function|return|if|else|for|while|class|import|export|from|async|await)\b/g, class: 'keyword' },
{ regex: /\b(true|false|null|undefined|NaN)\b/g, class: 'literal' },
];
let result = code;
for (const { regex, class: cls } of rules) {
result = result.replace(regex, `<span class="${cls}">$1</span>`);
}
return result;
}
8. Unicode & Internationalization
8.1 Matching Unicode Characters
javascript
// Match emoji
const text = 'Hello 👋 World 🌍!';
// Without 'u' flag — doesn't work correctly with surrogate pairs
const emoji = text.match(/[\u{1F600}-\u{1F9FF}]/gu);
console.log(emoji); // ['👋', '🌍']
// Unicode property escapes (ES2018)
const allEmoji = text.match(/\p{Emoji_Presentation}/gu);
console.log(allEmoji); // ['👋', '🌍']
8.2 Matching Scripts & Categories
javascript
// Match any letter from any language
const text = 'Hello مرحبا こんにちは 你好';
const letters = text.match(/\p{Letter}+/gu);
console.log(letters);
// ['Hello', 'مرحبا', 'こんにちは', '你好']
// Match only Arabic script
const arabic = text.match(/\p{Script=Arabic}+/gu);
console.log(arabic); // ['مرحبا']
// Match CJK (Chinese/Japanese/Korean)
const cjk = text.match(/[\p{Script=Han}\p{Script=Hiragana}\p{Script=Katakana}]+/gu);
console.log(cjk); // ['こんにちは', '你好']
9. Performance Tips
9.1 Compile Once, Use Many Times
javascript
// ❌ BAD: Regex compiled on every call
function findEmails(texts) {
return texts.filter(t => /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(t));
}
// ✅ GOOD: Regex compiled once
const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
function findEmails(texts) {
return texts.filter(t => emailRegex.test(t));
}
9.2 Avoid Catastrophic Backtracking
javascript
// ❌ DANGEROUS: Exponential backtracking on non-matching input
const badRegex = /^(a+)+$/;
// This hangs on: 'aaaaaaaaaaaaaaaaaaaaaa!'
// ✅ SAFE: Simplified, no nested quantifiers
const goodRegex = /^a+$/;
🛑 caution[!CAUTION] Nested quantifiers like
(a+)+,(a*)*, or(a|a)*can cause catastrophic backtracking — the regex engine tries exponentially many paths. Always test your patterns with non-matching inputs.
9.3 Use Specific Patterns
javascript
// ❌ SLOW: Overly broad
const slow = /.*@.*\..*/;
// ✅ FAST: Specific character classes
const fast = /[^\s@]+@[^\s@]+\.[^\s@]+/;
10. Quick Interview Q&A
| Question | Answer |
|---|---|
| test() vs match()? | test() returns boolean, match() returns match array or null. Use test() for simple validation. |
| Greedy vs lazy? | Greedy (*, +) matches as much as possible; lazy (*?, +?) matches as little as possible. |
| What is a lookahead? | (?=...) asserts what follows without consuming characters. Useful for complex validations. |
| Named groups? | (?<name>pattern) creates a named capture accessible via match.groups.name. |
Why double-escape in new RegExp()? | Strings process \ first. \d in a string is just d. Use \\d to pass \d to the regex engine. |
| What causes catastrophic backtracking? | Nested quantifiers like (a+)+ create exponential paths. Simplify or use atomic groups. |
| match() vs matchAll()? | match(/g/) returns strings only. matchAll() returns an iterator with full match objects including groups. |
What does the u flag do? | Enables full Unicode support. Required for \p{...} property escapes and correct surrogate pair handling. |
Regex Cheat Sheet
CHARACTERS
. Any character (except newline)
\d \D Digit / Non-digit
\w \W Word char / Non-word char
\s \S Whitespace / Non-whitespace
\b Word boundary
QUANTIFIERS
* 0 or more (greedy)
+ 1 or more (greedy)
? 0 or 1 (greedy)
*? +? Lazy versions
{n} Exactly n
{n,m} Between n and m
GROUPS
(...) Capture group
(?:...) Non-capture group
(?<n>..) Named group
\1 Backreference
ASSERTIONS
^ $ Start / End of string
(?=...) Positive lookahead
(?!...) Negative lookahead
(?<=...) Positive lookbehind
(?<!...) Negative lookbehind
FLAGS
g i m s u d v
Conclusion
Regular expressions are a critical skill that separates developers who struggle with text processing from those who handle it with ease:
- Validation: Use regex for emails, passwords, phone numbers, and URLs — but know the limitations
- Extraction: Named groups +
matchAll()make pulling structured data from text effortless - Transformation:
replace()with functions enables powerful text processing pipelines - Lookaround: Zero-width assertions let you validate complex conditions without over-matching
- Performance: Compile once, avoid nested quantifiers, and use specific character classes
The patterns in this guide cover the vast majority of regex use cases you'll encounter in real-world JavaScript development. Bookmark the cheat sheet, practice with the examples, and regex will become one of your most valued tools.
Happy coding! 🚀
🧠 Test Your Knowledge
Now that you've learned the concepts, let's see if you can apply them! Take this quick quiz to test your understanding.