next-forge
Complete guide to migrating from TypeScript 5 to TypeScript 6. Covers ESM-first module system changes, deprecated APIs, new strict type checks, and step-by-step migration strategies for large codebases.
TypeScript 6 introduces several breaking changes, the most significant being adjustments to the module system and deprecation of some older syntax. Understanding the scope of impact is essential before migrating.
The baseUrl configuration option is officially deprecated in TypeScript 6. The recommended approach is to use paths with root path aliases, or the imports field for intra-package path mapping, avoiding reliance on implicit path resolution.
Decorator syntax is further standardized in TypeScript 6, aligning with the ECMAScript standard. The behavior of the old experimentalDecorators mode may differ, so testing is necessary.
The type inference engine receives a major optimization in TypeScript 6, with type-checking speed improvements of 20-30% for large projects, along with more accurate inference for complex generics.
It is recommended to first upgrade to the latest TypeScript 5 version and fix all warnings before gradually upgrading to 6, using --allowJs and strict mode configurations to proceed in phases.