The JavaScript Regex Cheat Sheet: 10 Patterns That Cover 80 Percent of Your Use Cases

Regular expressions are one of those tools that look intimidating at first but become indispensable once you understand them. This guide covers the patterns you'll actually use in JavaScript projects — from form validation to parsing log files. The Basics You Need to Know First A regex in JavaScript looks like /pattern/flags . You can use it two ways: // Method 1: Regex literal (preferred for static patterns) const emailRegex = /^ [^\s @ ] +@ [^\s @ ] + \.[^\s @ ] +$/ ; // Method 2: RegExp constructor (use when pattern is dynamic) const term = " error " ; const logRegex = new RegExp ( ` \\ b ${ term } \\ b` , " gi " ); The most important flags: g — global, find all matches (not just the first) i — case-insensitive m — multiline, ^ and $ match line start/end s — dotAll, . matches newlines too The 10 Patterns That Cover 80% of Use Cases 1. Email Validation const isEmail = ( str ) => /^ [^\s @ ] +@ [^\s @ ] + \.[^\s @ ] +$/ . test ( str ); isEmail ( " user@example.com " ); // true isEmail