TypeScript 5.5 Introduces Inferred Type Predicates

Microsoft has released TypeScript 5.5 with several powerful new features that improve type safety and developer productivity. The standout feature is inferred type predicates, which automatically narrow types based on control flow.

Inferred Type Predicates

Previously, developers had to manually write type predicates for filter operations. TypeScript 5.5 now infers these automatically, making array filtering more type-safe without extra code.

This means filtering arrays with methods like filter will now properly narrow types without explicit type predicates, reducing boilerplate and potential errors.

Const Type Parameters

The new const type parameters feature allows you to preserve literal types in generic functions, similar to how as const works. This is particularly useful for library authors building type-safe APIs.

Performance Improvements

TypeScript 5.5 includes significant performance optimizations:

• 30% faster type checking for large codebases
• Reduced memory consumption during compilation
• Improved watch mode responsiveness

Regular Expression Syntax Checking

The compiler now validates regular expression syntax at compile time, catching common regex errors before runtime and providing helpful error messages.