Is the FixTools Regex Tester the same as JavaScript regex?

Yes. The tester runs in your browser using the JavaScript engine (V8 in Chrome, SpiderMonkey in Firefox). Patterns that work in the tester work identically in your browser JavaScript and Node.js code.

Does JavaScript regex support lookbehind?

Yes, since ES2018. JavaScript supports both positive (?<=...) and negative (?<!...) lookbehinds. These are supported in all modern browsers and Node.js 10+.

What is the u (unicode) flag in JavaScript?

The u flag enables full Unicode mode. It makes \p{...} Unicode property escapes work and ensures that multi-byte Unicode characters (like emoji) are counted as single characters, not two code units.

How is JavaScript regex different from Python?

Key differences: JavaScript uses flags like s for dotAll (Python uses re.DOTALL), JavaScript named groups use (? ...) (Python uses (?P ...)), and JavaScript lacks \A/\Z anchors (use ^ and $ with m flag instead).

Can I test regex for Node.js with this tool?

Yes. Node.js uses the V8 JavaScript engine, which is the same engine your browser uses. Patterns that work in the FixTools tester work identically in Node.js.

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Test JavaScript Regex Online — Native JS Engine

Q: What is the u (unicode) flag in JavaScript?

The u flag enables full Unicode mode. It makes \p{...} Unicode property escapes work and ensures that multi-byte Unicode characters (like emoji) are counted as single characters, not two code units.

Q: How is JavaScript regex different from Python?

Key differences: JavaScript uses flags like s for dotAll (Python uses re.DOTALL), JavaScript named groups use (? ...) (Python uses (?P ...)), and JavaScript lacks \A/\Z anchors (use ^ and $ with m flag instead).

Q: Can I test regex for Node.js with this tool?

Yes. Node.js uses the V8 JavaScript engine, which is the same engine your browser uses. Patterns that work in the FixTools tester work identically in Node.js.

JavaScript has its own regex flavour with specific syntax and features — including named captures, unicode mode, and the dotAll flag — that differ from Python or PCRE. FixTools Regex Tester runs in the browser, so it uses the native JavaScript regex engine: what you see in the tester is exactly what you get in your JS code.

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Processing: In your browser
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Uses the native JavaScript (V8) regex engine

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Supports ES2018+ features: named groups, dotAll, unicode

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Matches behave exactly as in Node.js and browser code

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How to use this tool

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Enter your JavaScript regex pattern and test string. The engine behaviour is identical to running new RegExp(pattern, flags).exec(string) in Node.js or Chrome.

How It Works

Step-by-step guide to test javascript regex online — native js engine:

1
Enter your JS regex pattern
Type your pattern without JavaScript literal delimiters (/ /) — just the pattern text itself, e.g. \d{3}-\d{4}.
2
Set JavaScript-specific flags
Choose from: g (global), i (case-insensitive), m (multiline), s (dotAll — makes . match newlines), u (unicode), and y (sticky).
3
Enter your test string
Paste the string your JS code will process.
4
Review results
Matches behave identically to the JavaScript RegExp engine. Named capture groups appear by name in the results.