Published on May 22, 2023
Microsoft has released the latest version of its popular programming language, TypeScript 5.1, which is now available in a release candidate stage. The update includes a number of significant changes, including easier implicit returns for undefined-returning functions and greater type flexibility for getters and setters. These properties can now have unrelated types as long as they have explicit type annotations.
TypeScript 5.1 also introduces new features such as refactoring support for moving declarations to existing files, allowing developers to easily reorganize their code. Additionally, the release candidate changes the behavior for init hooks in decorators and emit behavior under isolatedModules.
The changes aim to fix the frustration and complications associated with the return statements for undefined functions, as well as to improve the flexibility of types for get and set accessor properties. With these enhancements, TypeScript continues to be a popular choice for developers looking to build robust and scalable applications. The final release of TypeScript 5.1 is expected to be available on May 30.
TypeScript 5.1 features a number of enhancements to the coding language. A new feature in TypeScript 5.1 is the ability to use implicit returns for undefined-returning functions without requiring a return statement. This solves the issue of only void-returning and any-returning functions being able to have no return statements. As a result, even if the developer explicitly indicated that the function returned undefined, at least one return statement was required.
There was a problem if an API expected a function to return undefined, in which case there should be at least one explicit return of undefined or a return statement and an explicit annotation. According to Microsoft, this behaviour was confusing and frustrating. Furthermore, TypeScript 5.1 infers undefined for a function’s return type when there is no return expression and the function is passed to something that expects an undefined return value.
In TypeScript 5.1, completely unrelated types can also be used for get and set accessor properties, provided they are annotated with explicit types. In TypeScript 4.3, a get and set accessor pair may specify two different types.
