TypeScript 5.0 Drops Legacy Decorators: What Teams Must Know Before Migrating

TypeScript 5.0 and later ships with TC39 standard decorators by default, making the older experimentalDecorators implementation increasingly obsolete. The two systems are fundamentally incompatible — not interchangeable — as the decorator signature, metadata handling, and prototype mutation approaches all changed significantly. Parameter decorators have been removed entirely, and metadata collection now relies on a context object rather than the reflect-metadata library. Migration requires rewriting decorator functions one category at a time, starting with class decorators, and using conditional exports to allow both systems to coexist during the transition. Experts recommend migrating incrementally when adding new features rather than attempting a full codebase rewrite at once.