Read a compile error and recover with a corrected pattern
Keep the source text while correcting an invalid expression, then check fresh results.
For operators
Keep the source text while correcting an invalid expression, then check fresh results. This is isolated practice with invented records. Nothing is uploaded or written into a live system.
Read these instructions on any device. Watch or practise a chapter on a desktop or laptop, with a desktop or mobile application layout. Demonstrations use sample data and simulated scanners.
Read a compile error and recover with a corrected pattern
- Enter an incomplete character class
Enter an incomplete character class.
An opening bracket without its closing bracket is not a complete JavaScript pattern.
- Read the compile error
Read the compile error.
No match result is produced from an invalid pattern. The text stays available so you can correct the pattern deliberately.
- Complete the character class
Complete the character class.
This pattern now means one uppercase ASCII letter. Changing the input discards the previous result.
- Enter an item prefix
Enter an item prefix.
The default global flag will find both letters. JavaScript results still do not establish PCRE or .NET behaviour.
- Run a fresh worker
Run a fresh worker.
The corrected expression produces two matches in a new disposable worker. Stop is available during a slow run, and the work limit protects the page.
Review the result and its limits before using it in another application.