Bloomberg TS5.5-beta feedback

Acknowledgement

• I acknowledge that issues using this template may be closed without further explanation at the maintainer's discretion.

Comment

We are in the process of evaluating the impact of TS 5.5 beta on Bloomberg code. Below are preliminary findings.

Overall this looks to be a low-impact release. The following changes were observed and seem to either be benign in nature or else improvements:

Stricter type-checking of partial objects

We observed one project with a new type error in 5.5-beta, seemingly due to an improvement in type-checking for partials.

A minimal reproduction is here.

Improved narrowing of Array.isArray result

We observed for one project a new type error from trying to compare a string with an array after an Array.isArray check. The generics involved make a minimal reproduction infeasible but the essence of the code is:

if (Array.isArray(foo)) {
     If (foo !== "something") // raises a new error for some complex foo
}

Exports are hoisted to the top of a module

Module exports seem to be hoisted to the top of modules now. No runtime impact observed.

Object.defineProperty(exports, "__esModule", { value: true });
+exports.foo = foo;
 function foo() {
     // …
 }
-exports.foo = foo;

El issue no menciona archivos ni pruebas del repositorio; comienza con la reproducción mínima vinculada de TypeScript 5.5 beta y compara el comportamiento de comprobación de tipos descrito con las release notes. Después, investiga el ejemplo de narrowing de Array.isArray y el orden de los exports emitidos; se considerará terminado cuando los hallazgos se confirmen como comportamiento esperado o como regresiones accionables.