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Note section for Symbol.metadata in the plugin-proposal-decorators doc #2967

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Note section for Symbol.metadata in the plugin-proposal-decorators doc #2967

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20 changes: 20 additions & 0 deletions docs/plugin-proposal-decorators.md
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Expand Up @@ -76,6 +76,26 @@ require("@babel/core").transformSync("code", {
]
});
```
## Note on `Symbol.metadata`

When using decorators which either access or modify the metadata in the decorator context, you may need to use `Symbol.metadata`. However, `Symbol.metadata` is not defined globally by default because it is part of an experimental proposal (https://github.com/tc39/proposal-decorator-metadata).

To ensure `Symbol.metadata` is available globally and matches the symbol used by the Babel decorators plugin during transpilation, you need to include a polyfill that defines it.

### Steps to Include the Polyfill

Install `core-js`
```shell npm2yarn
npm install core-js
```

Import the Metadata Polyfill

```js title="Javascript"
import 'core-js/proposals/decorator-metadata-v2.js';
```

Note: This import must come before any code that uses decorators or accesses `Symbol.metadata`.

## Options

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