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Also featured in TypeScript 6.0 is support for the es2025 option for both target and lib, less context sensitivity on this-less functions, and new types for Temporal, which provide standard objects and functions for working with dates and times. With the --stableTypeOrdering flag, the type ordering behavior of TypeScript 6.0 matches that of TypeScript 7.0, reducing the number of differences between the two codebases. Microsoft does not necessarily encourage using this flag all the time as it can add a substantial slowdown to type checking (up to 25% depending on the codebase).
With TypeScript 6.0’s es2025, option, the new target adds new types for built-in APIs (e.g. RegExp.escape) and moves a few declarations from esnext into es2025. With this-less functions, if this is never actually used in a function, then it is not considered contextually sensitive. That means these functions will be seen as higher priority when it comes to type inference. For Temporal, the long-awaited ECMAScript Temporal proposal has reached stage 3 and is expected to be added to JavaScript in the near future, Rosenwasser said. TypeScript 6.0 now includes built-in types for the Temporal API, so developers can start using it in TypeScript code via --target esnext or "lib": ["esnext"] or the more granular temporal.esnext.
Other new features and improvements in TypeScript 6.0:
