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Kotlin/JS doc update for 2.3.0 release #5192

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72 changes: 48 additions & 24 deletions docs/topics/js/js-to-kotlin-interop.md
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Expand Up @@ -213,35 +213,59 @@ kotlin {

2. Enable the `BigInt` type. See how to enable it in [Use of `BigInt` type to represent Kotlin's `Long` type](#use-bigint-type-to-represent-kotlin-s-long-type).
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@zamulla zamulla Nov 21, 2025

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This is not about the change, but for consistency: The link text does not match the corresponding heading, should it? Both are grammatically correct, it just looks odd that they are different.


### Use `BigInt64Array` type to represent Kotlin's `LongArray` type
<primary-label ref="experimental-general"/>

Kotlin/JS uses JavaScript's built-in `BigInt64Array` type
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@zamulla zamulla Nov 21, 2025

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If I need to enable this feature, it should probably be "can use", not "uses"?

to represent Kotlin's `LongArray` values when compiling to JavaScript.

To enable support for the `BigInt64Array` type, you need to add the following compiler option to your
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Suggested change
To enable support for the `BigInt64Array` type, you need to add the following compiler option to your
To enable support for the `BigInt64Array` type, add the following compiler option to your

`build.gradle(.kts)` file:

```kotlin
// build.gradle.kts
kotlin {
js {
...
compilerOptions {
freeCompilerArgs.add("-Xes-long-as-bigint")
}
}
}
```

This feature is [Experimental](components-stability.md#stability-levels-explained). Share your feedback in our issue tracker,
[YouTrack](https://youtrack.jetbrains.com/issue/KT-79284/Use-BigInt64Array-for-LongArray).

## Kotlin types in JavaScript

See how Kotlin types are mapped to JavaScript ones:

| Kotlin | JavaScript | Comments |
|------------------------------------------------------------------|---------------------------|---------------------------------------------------------------------------------------|
| `Byte`, `Short`, `Int`, `Float`, `Double` | `Number` | |
| `Char` | `Number` | The number represents the character's code. |
| Kotlin | JavaScript | Comments |
|------------------------------------------------------------------|---------------------------|---------------------------------------------------------------------------------------------------------|
| `Byte`, `Short`, `Int`, `Float`, `Double` | `Number` | |
| `Char` | `Number` | The number represents the character's code. |
| `Long` | `BigInt` | Needs the [`-Xes-long-as-bigint` compiler option](compiler-reference.md#xes-long-as-bigint) configured. |
| `Boolean` | `Boolean` | |
| `String` | `String` | |
| `Array` | `Array` | |
| `ByteArray` | `Int8Array` | |
| `ShortArray` | `Int16Array` | |
| `IntArray` | `Int32Array` | |
| `CharArray` | `UInt16Array` | Carries the property `$type$ == "CharArray"`. |
| `FloatArray` | `Float32Array` | |
| `DoubleArray` | `Float64Array` | |
| `LongArray` | `Array<kotlin.Long>` | Carries the property `$type$ == "LongArray"`. Also see Kotlin's Long type comment. |
| `BooleanArray` | `Int8Array` | Carries the property `$type$ == "BooleanArray"`. |
| `List`, `MutableList` | `KtList`, `KtMutableList` | Exposes an `Array` via `KtList.asJsReadonlyArrayView` or `KtMutableList.asJsArrayView`. |
| `Map`, `MutableMap` | `KtMap`, `KtMutableMap` | Exposes an ES2015 `Map` via `KtMap.asJsReadonlyMapView` or `KtMutableMap.asJsMapView`. |
| `Set`, `MutableSet` | `KtSet`, `KtMutableSet` | Exposes an ES2015 `Set` via `KtSet.asJsReadonlySetView` or `KtMutableSet.asJsSetView`. |
| `Unit` | Undefined | Exportable when used as return type, but not when used as parameter type. |
| `Any` | `Object` | |
| `Throwable` | `Error` | |
| `enum class Type` | `Type` | Enum entries are exposed as static class properties (`Type.ENTRY`). |
| Nullable `Type?` | `Type | null | undefined` | |
| All other Kotlin types, except for those marked with `@JsExport` | Not supported | Includes Kotlin's [unsigned integer types](unsigned-integer-types.md). |
| `Boolean` | `Boolean` | |
| `String` | `String` | |
| `Array` | `Array` | |
| `ByteArray` | `Int8Array` | |
| `ShortArray` | `Int16Array` | |
| `IntArray` | `Int32Array` | |
| `CharArray` | `UInt16Array` | Carries the property `$type$ == "CharArray"`. |
| `FloatArray` | `Float32Array` | |
| `DoubleArray` | `Float64Array` | |
| `LongArray` | `BigInt64Array` | |
| `BooleanArray` | `Int8Array` | Carries the property `$type$ == "BooleanArray"`. |
| `List`, `MutableList` | `KtList`, `KtMutableList` | Exposes an `Array` via `KtList.asJsReadonlyArrayView` or `KtMutableList.asJsArrayView`. |
| `Map`, `MutableMap` | `KtMap`, `KtMutableMap` | Exposes an ES2015 `Map` via `KtMap.asJsReadonlyMapView` or `KtMutableMap.asJsMapView`. |
| `Set`, `MutableSet` | `KtSet`, `KtMutableSet` | Exposes an ES2015 `Set` via `KtSet.asJsReadonlySetView` or `KtMutableSet.asJsSetView`. |
| `Unit` | Undefined | Exportable when used as return type, but not when used as parameter type. |
| `Any` | `Object` | |
| `Throwable` | `Error` | |
| `enum class Type` | `Type` | Enum entries are exposed as static class properties (`Type.ENTRY`). |
| Nullable `Type?` | `Type | null | undefined` | |
| All other Kotlin types, except for those marked with `@JsExport` | Not supported | Includes Kotlin's [unsigned integer types](unsigned-integer-types.md). |

Additionally, it is important to know that:

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