TypeScript 4.9 is a language that builds on JavaScript by adding types and type-checking. It can also power other tooling like auto-completion, go-to-definition, and refactorings in the editor.
Table of contents
What’s New Since the Beta and RC?The satisfies OperatorUnlisted Property Narrowing with the in OperatorAuto-Accessors in ClassesChecks For Equality on NaNFile-Watching Now Uses File System Events"Remove Unused Imports" and "Sort Imports" Commands for EditorsGo-to-Definition on return KeywordsPerformance ImprovementsCorrectness Fixes and Breaking Changessubstitute Replaced With constraint on SubstitutionType sWhat’s NextSort: