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Adds a note in the 4.3 release notes for the useDefineForClassFields default change #2008

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Aug 31, 2021
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Adds a note in the 4.3 release notes for the useDefineForClassFields default change #2008

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Adds a note in the 4.3 release notes for the useDefineForClassFields …
orta Aug 31, 2021
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Fixes the year
orta Aug 31, 2021
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6 changes: 6 additions & 0 deletions packages/documentation/copy/en/release-notes/TypeScript 4.3.md
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Expand Up @@ -774,6 +774,12 @@ This is discussed [in some detail here](https://github.com/microsoft/TypeScript-

https://github.com/microsoft/TypeScript-DOM-lib-generator/issues/991

### `useDefineForClassFields` now defaults to true on `esnext` and eventually on `es2022`

In 2021 the class fields feature was added into the JavaScript specification with behavior which differed from how TypeScript had implemented it. In preparation for this, in TypeScript 3.7, a flag was added ([`useDefineForClassFields`](https://www.typescriptlang.org/tsconfig#useDefineForClassFields)) to migrate to emitted JavaScript to match the JavaScript standard behavior.

Now that the feature is in JavaScript we are changing the default to `true` for ES2022 and above, including ESNext.

### Errors on Always-Truthy Promise Checks

Under `strictNullChecks`, using a `Promise` that always appears to be defined within a condition check is now considered an error.
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