Usage in Deno
```typescript import * as mod from "node:node__wasi.d.ts"; ```> [!WARNING] Deno compatibility
> All exports are non-functional stubs.
**The `node:wasi` module does not currently provide the**
**comprehensive file system security properties provided by some WASI runtimes.**
**Full support for secure file system sandboxing may or may not be implemented in**
**future. In the mean time, do not rely on it to run untrusted code.**
The WASI API provides an implementation of the [WebAssembly System Interface](https://wasi.dev/) specification. WASI gives WebAssembly applications access to the underlying
operating system via a collection of POSIX-like functions.
```js
import { readFile } from 'node:fs/promises';
import { WASI } from 'node:wasi';
import { argv, env } from 'node:process';
const wasi = new WASI({
version: 'preview1',
args: argv,
env,
preopens: {
'/local': '/some/real/path/that/wasm/can/access',
},
});
const wasm = await WebAssembly.compile(
await readFile(new URL('./demo.wasm', import.meta.url)),
);
const instance = await WebAssembly.instantiate(wasm, wasi.getImportObject());
wasi.start(instance);
```
To run the above example, create a new WebAssembly text format file named `demo.wat`:
```text
(module
;; Import the required fd_write WASI function which will write the given io vectors to stdout
;; The function signature for fd_write is:
;; (File Descriptor, *iovs, iovs_len, nwritten) -> Returns number of bytes written
(import "wasi_snapshot_preview1" "fd_write" (func $fd_write (param i32 i32 i32 i32) (result i32)))
(memory 1)
(export "memory" (memory 0))
;; Write 'hello world\n' to memory at an offset of 8 bytes
;; Note the trailing newline which is required for the text to appear
(data (i32.const 8) "hello world\n")
(func $main (export "_start")
;; Creating a new io vector within linear memory
(i32.store (i32.const 0) (i32.const 8)) ;; iov.iov_base - This is a pointer to the start of the 'hello world\n' string
(i32.store (i32.const 4) (i32.const 12)) ;; iov.iov_len - The length of the 'hello world\n' string
(call $fd_write
(i32.const 1) ;; file_descriptor - 1 for stdout
(i32.const 0) ;; *iovs - The pointer to the iov array, which is stored at memory location 0
(i32.const 1) ;; iovs_len - We're printing 1 string stored in an iov - so one.
(i32.const 20) ;; nwritten - A place in memory to store the number of bytes written
)
drop ;; Discard the number of bytes written from the top of the stack
)
)
```
Use [wabt](https://github.com/WebAssembly/wabt) to compile `.wat` to `.wasm`
```bash
wat2wasm demo.wat
```
c
WASI
> [!WARNING] Deno compatibility
> This symbol is a non-functional stub.
The `WASI` class provides the WASI system call API and additional convenience
methods for working with WASI-based applications. Each `WASI` instance
represents a distinct environment.
I
WASIOptions
> [!WARNING] Deno compatibility
> This symbol is a non-functional stub.