index.js

import { SwiftRuntime } from "javascript-kit-swift";
import { WASI } from "@wasmer/wasi";
import { WasmFs } from "@wasmer/wasmfs";

const swift = new SwiftRuntime();
// Instantiate a new WASI Instance
const wasmFs = new WasmFs();

// Output stdout and stderr to console
const originalWriteSync = wasmFs.fs.writeSync;
wasmFs.fs.writeSync = (fd, buffer, offset, length, position) => {
    const text = new TextDecoder("utf-8").decode(buffer);

    // Filter out standalone "\n" added by every `print`, `console.log`
    // always adds its own "\n" on top.
    if (text !== "\n") {
        switch (fd) {
            case 1:
                console.log(text);
                break;
            case 2:
                console.error(text);
                break;
        }
    }
    return originalWriteSync(fd, buffer, offset, length, position);
};

let wasi = new WASI({
    args: [],
    env: {},
    bindings: {
        ...WASI.defaultBindings,
        fs: wasmFs.fs,
    },
});

const startWasiTask = async () => {
    // Fetch our Wasm File
    const response = await fetch("JavaScriptKitExample.wasm");
    const responseArrayBuffer = await response.arrayBuffer();

    // Instantiate the WebAssembly file
    const wasm_bytes = new Uint8Array(responseArrayBuffer).buffer;
    let { instance } = await WebAssembly.instantiate(wasm_bytes, {
        wasi_snapshot_preview1: wasi.wasiImport,
        javascript_kit: swift.importObjects(),
    });

    swift.setInstance(instance);
    // Start the WebAssembly WASI instance!
    wasi.start(instance);
};
startWasiTask();