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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Breaking change to default useDefineForClassFields to true should be clearly documented","articleBody":"# Bug Report\r\n\r\nIn some contexts (I'm not sure exactly which, but `\"target\": \"esnext\"` does it) `useDefineForClassFields` now defaults to `true`.\r\n\r\nThis is a breaking change for any code with `\"experimentalDecorators\": true`, but I can't find documentation for it anywhere.\r\n\r\n### 🔎 Search Terms\r\n\r\n`useDefineForClassFields` `experimentalDecorators`\r\n\r\n### 🕗 Version & Regression Information\r\n\r\nThe `useDefineForClassFields` flag was introduced in 3.7 but defaulted to `false`: https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#the-usedefineforclassfields-flag-and-the-declare-property-modifier\r\n\r\nThis is a known breaking change when using decorators: https://github.com/microsoft/TypeScript/issues/35081\r\n\r\nIn https://github.com/microsoft/TypeScript/pull/42663 this was changed so that in some contexts `useDefineForClassFields` now defaults to `true`.\r\n\r\nThere is no mention of `useDefineForClassFields` on https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-4.html (or 4.3, or 4.2, or 4.1)\r\n\r\nThere is a mention on 4.0, but in as different context and the default change isn't mentioned https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-0.html#properties-overriding-accessors-and-vice-versa-is-an-error\r\n\r\nThis is a breaking change for all projects that use decorators, it should be clearly identified as a breaking change.\r\n\r\n### ⏯ Playground Link\r\n\r\nThis is missing documentation\r\n\r\n### 💻 Code\r\n\r\nThis is missing documentation\r\n\r\n### 🙁 Actual behavior\r\n\r\nRelease notes don't mention the breaking change. I'm not even sure which release they should be in.\r\n\r\n### 🙂 Expected behavior\r\n\r\nRelease notes should clearly document the breaking change.\r\n","author":{"url":"https://github.com/KeithHenry","@type":"Person","name":"KeithHenry"},"datePublished":"2021-08-31T07:44:39Z","url":"https://github.com/microsoft/TypeScript/issues/45653"}