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Updated Breaking Changes (markdown)

Daniel Rosenwasser 2020-05-12 10:04:57 -07:00
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Breaking-Changes.md

@ -181,6 +181,38 @@ In practice, we don't expect this to break much existing code.
You can see the specific changes in [the original pull request](https://github.com/microsoft/TypeScript/pull/37124).
## Exports Now Use Getters for Live Bindings
When targeting module systems like CommonJS in ES5 and above, TypeScript will use get accessors to emulate live bindings.
https://github.com/microsoft/TypeScript/pull/35967
## Exports are Hoisted and Initially Assigned
TypeScript now hoists exported declarations to the top of the file when targeting module systems like CommonJS in ES5 and above. For example, code like
```ts
export * from "mod";
export const nameFromMod = 0;
```
previously had output like
```ts
__exportStar(exports, require("mod"));
exports.nameFromMod = 0;
```
However, because exports now use `get`-accessors, this assignment would throw because `__exportStar` now makes get-accesors which can't be overridden with a simple assignment. Instead, TypeScript 3.9 emits the following:
```ts
exports.nameFromMod = void 0;
__exportStar(exports, require("mod"));
exports.nameFromMod = 0;
```
See [the original pull request](https://github.com/microsoft/TypeScript/pull/37093) for more information.
# TypeScript 3.8
## Stricter Assignability Checks to Unions with Index Signatures