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Add fixed arguments case to as decorator syntax lookup entry #1021

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May 4, 2025
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Add fixed arguments case to as decorator syntax lookup entry #1021

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22 changes: 22 additions & 0 deletions misc_docs/syntax/decorator_as.mdx
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Expand Up @@ -82,6 +82,28 @@ let somethingElse = null;

Read more about the [`@as` decorator and variants](variant.md#valid-as-payloads).

## Adding fixed argument values to external functions
You can leverage the `@as` decorator to add fixed values for external function arguments. You then do not need to supply a value for that argument.

<CodeTab labels={["ReScript", "JS Output"]}>

```res
@module("fs")
external readFileSyncUtf8: (string, @as(json`{encoding: "utf8"}`) _) => string = "readFileSync"

let contents = readFileSyncUtf8("./someFile.txt")
```

```js
import * as Fs from "fs";

let contents = Fs.readFileSync("./someFile.txt", {encoding: "utf8"});
```

</CodeTab>

Read more about [fixed arguments in functions](bind-to-js-function.md#fixed-arguments).

### References

* [Bind Using ReScript Record](/docs/manual/latest/bind-to-js-object#bind-using-rescript-record)
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