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What are the basics of regular expressions in JavaScript?

Q: What are the basics of regular expressions in JavaScript?

**Core concept (TL;DR).** A regular expression describes a **text pattern**. In JS you write one as a literal between slashes ( /pattern/flags ) or with new RegExp() , then use methods like test (boolean), match / matchAll (extract), and replace (substitute). Flags like g (global), i (case-insensitive), and m (multiline) tune the matching. A pattern + flags, applied with test / match / replace <rect x="20" y="38" width="150" height="24" rx="5" fill="#3b82f6" fill-opacity="0.10" stroke="

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