| Supported | Rust                            | Fastcall | V8          | Notes                                                                                                                                                                                            |
| --------- | ------------------------------- | -------- | ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| X         | bool                            | X        | Bool        |                                                                                                                                                                                                  |
| X         | i8                              | X        | Int32       |                                                                                                                                                                                                  |
| X         | u8                              | X        | Uint32      |                                                                                                                                                                                                  |
| X         | i16                             | X        | Int32       |                                                                                                                                                                                                  |
| X         | u16                             | X        | Uint32      |                                                                                                                                                                                                  |
| X         | i32                             | X        | Int32       |                                                                                                                                                                                                  |
| X         | u32                             | X        | Uint32      |                                                                                                                                                                                                  |
| X         | #[smi] ResourceId               | X        | Int32       | SMI is internally represented as a signed integer, but unsigned `#[smi]` types will be bit-converted to unsigned values for the Rust call. JavaScript code will continue to see signed integers. |
| X         | #[bigint] i64                   | X        | BigInt      |                                                                                                                                                                                                  |
| X         | #[bigint] u64                   | X        | BigInt      |                                                                                                                                                                                                  |
| X         | #[bigint] isize                 | X        | BigInt      |                                                                                                                                                                                                  |
| X         | #[bigint] usize                 | X        | BigInt      |                                                                                                                                                                                                  |
| X         | #[number] i64                   | X        | Number      | Result must fit within `Number.MIN_SAFE_INTEGER` and `Number.MAX_SAFE_INTEGER`                                                                                                                   |
| X         | #[number] u64                   | X        | Number      | Result must fit within `Number.MIN_SAFE_INTEGER` and `Number.MAX_SAFE_INTEGER`                                                                                                                   |
| X         | #[number] isize                 | X        | Number      | Result must fit within `Number.MIN_SAFE_INTEGER` and `Number.MAX_SAFE_INTEGER`                                                                                                                   |
| X         | #[number] usize                 | X        | Number      | Result must fit within `Number.MIN_SAFE_INTEGER` and `Number.MAX_SAFE_INTEGER`                                                                                                                   |
| X         | f32                             | X        | Number      |                                                                                                                                                                                                  |
| X         | f64                             | X        | Number      |                                                                                                                                                                                                  |
| X         | #[string] String                |          | String      |                                                                                                                                                                                                  |
| X         | #[string] &str                  |          | String      |                                                                                                                                                                                                  |
| X         | #[string] Cow<str>              |          | String      |                                                                                                                                                                                                  |
| X         | #[string(onebyte)] Cow<[u8]>    |          | String      |                                                                                                                                                                                                  |
| X         | #[arraybuffer] V8Slice<u8>      |          | ArrayBuffer |                                                                                                                                                                                                  |
| X         | #[arraybuffer] Vec<u8>          |          | ArrayBuffer |                                                                                                                                                                                                  |
| X         | #[arraybuffer] Box<[u8]>        |          | ArrayBuffer |                                                                                                                                                                                                  |
| X         | #[arraybuffer] bytes::BytesMut  |          | ArrayBuffer |                                                                                                                                                                                                  |
| X         | #[buffer] V8Slice<u8>           |          | Uint8Array  |                                                                                                                                                                                                  |
| X         | #[buffer] Vec<u8>               |          | Uint8Array  |                                                                                                                                                                                                  |
| X         | #[buffer] Box<[u8]>             |          | Uint8Array  |                                                                                                                                                                                                  |
| X         | #[buffer] bytes::BytesMut       |          | Uint8Array  |                                                                                                                                                                                                  |
| X         | #[buffer] V8Slice<u32>          |          | Uint32Array |                                                                                                                                                                                                  |
|           | #[buffer] Vec<u32>              |          | Uint32Array |                                                                                                                                                                                                  |
|           | #[buffer] Box<[u32]>            |          | Uint32Array |                                                                                                                                                                                                  |
| X         | *const std::ffi::c_void         | X        | External    |                                                                                                                                                                                                  |
| X         | *mut std::ffi::c_void           | X        | External    |                                                                                                                                                                                                  |
| X         | v8::Local<v8::Value>            |          | any         |                                                                                                                                                                                                  |
| X         | v8::Local<v8::**V8**>           |          | **V8**      |                                                                                                                                                                                                  |
| X         | ToV8Type                        |          | any         | Any type that implements `deno_core::covert::ToV8`.                                                                                                                                              |
| X         | (ToV8Type, ToV8Type)            |          | any         | Any type that implements `deno_core::covert::ToV8`.                                                                                                                                              |
| X         | #[serde] SerdeType              |          | any         | ⚠️ Legacy & not recommended, use `ToV8` trait and macros instead.                                                                                                                                 |
| X         | #[serde] (SerdeType, SerdeType) |          | any         | ⚠️ Legacy & not recommended, use `ToV8` trait and macros instead.                                                                                                                                 |