What is a positive lookahead in regular expressions?

A positive lookahead `(?=...)` asserts that a given sub-pattern immediately follows the current match position without including those characters in the returned match.

Updated: August 2026 • Verified v1.2

JavaScript Regular Expression Cheat Sheet & Tester

Q: What is the difference between \d and \D in regex?

`\d` matches any digit character (0-9), while `\D` matches any character that is NOT a digit.

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RegExp Engine: /pattern/flags ➔ RegExp.prototype.test(string)

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Understanding Your Results

Provides a searchable master directory of regex tokens with descriptions, 1-click token copy, and a live pattern vs string test validator.

Practical Guidance & Next Steps

Lookaheads `(?=...)` and lookbehinds `(?<=...)` match patterns without consuming characters from the target string.

What is this?

A developer reference utility that catalogs JavaScript regular expression tokens and provides an instant pattern testing sandbox.

How does it work?

1. Search for regex tokens or browse categories (Character Classes, Quantifiers, Lookarounds, Anchors). 2. Test regex patterns against sample strings in the sandbox. 3. Copy regex tokens in 1 click.