Regex Testing Primer for JavaScript Developers

Regular expressions are powerful, but small changes can alter matching behavior in surprising ways.

Test with real examples

Use examples that include expected matches, near misses, empty values, and punctuation. This helps prevent overly broad patterns.

Understand flags

The g flag finds multiple matches, i ignores case, and m changes line behavior. Flags are part of the pattern's behavior and should be tested too.

Prefer readable patterns

If a regex becomes difficult to explain, consider splitting the logic into smaller validation steps.