Advanced TypeScript skills learned through hands-on practice

Due to a current program error, those who have newly registered for a course or changed their nickname are having trouble connecting.

We will revise it and notify you again by tomorrow (the 8th). We apologize for any inconvenience.

New or changed features since TypeScript 4.9

1. satisfaction

2. Decorator

Updated! I hope it helps many people 👨‍💻