Open
Description
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:
Change | Impacts | Release notes | Packages affected |
---|---|---|---|
Stricter type-checking of partial objects | Type checker | This may be caused by improved type predicates | 1 |
Improved narrowing of Array.isArray result |
Type checker | This may be caused by improved type predicates | 1 |
Exports are hoisted to the top of a module | Emitted JS | Not announced | Most |
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;