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Fix "SyntaxError: Invalid regular expression"

Solve JavaScript regex compilation crashes caused by unescaped special characters.

The Problem (Error Root Cause)Exception

Creating a RegExp object throws `SyntaxError: Invalid regular expression`. This occurs when you dynamically pass user input into `new RegExp()` without escaping special regex characters (like `[`, `(`, `*`, `?`).

Identified via runtime validation & stack traces

The Solution (Step-by-Step Fix)Verified

Always escape dynamic strings before passing them into `new RegExp()`. A simple replace function can escape all reserved characters.

Deterministic, non-destructive resolution

Code Standard: Bad Pattern vs Verified Fix

Live Syntax

Anti-Pattern vs Verified Fix

1// ❌ Bad: User input containing a '+' crashes the regex
2const search = "C++";
3const regex = new RegExp(search); // Crashes
4 
5// ✅ Good: Escaped input
6const escapeRegExp = (str) => str.replace(/[.*+?^$\{\}()|[\]\\]/g, '\\$&');
7const regex = new RegExp(escapeRegExp("C++"));

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Frequently Asked Questions

Q:Why does literal syntax /pattern/ not crash?

Literal syntax is validated at compile time by the JavaScript engine. new RegExp() compiles at runtime based on string values.

Q:How can I test complex regex safely?

Use our Regex Tester to validate patterns and groups in real time.