WASM in VSCode Extension

vscode_wasm_async.ts

import * as vscode from 'vscode';
import {promises as fs} from 'fs';
import * as path from 'path';

export function activate(context: vscode.ExtensionContext) {
    context.subscriptions.push(vscode.commands.registerCommand('wasmtest.helloWorld', async () => {
        const wasm = await load_wasm(path.join(context.extensionPath, 'media', 'bla.wasm'));
        const exports: any = wasm.exports; // not sure how static typing is supposed to work here
        const c_str = exports.greeting();
        const js_str = c_to_js_string(c_str, exports.memory.buffer);
        vscode.window.showInformationMessage("From WASM: " + js_str);
    }));
}

async function load_wasm(wasm_path: string): Promise<WebAssembly.Instance> {
    const wasm_bytes = new Uint8Array(await fs.readFile(wasm_path));
    const wasm = await WebAssembly.instantiate(wasm_bytes, {});
    return wasm.instance;
}

function c_to_js_string(c_str: number, mem: ArrayBuffer): string {
    const bytes = new Uint8Array(mem, c_str);
    let str = "";
    for (let i = 0; bytes[i]; i++) {
        str += String.fromCharCode(bytes[i]);
    }
    return str;
}

export function deactivate() {}

vscode_wasm_extension.ts

import * as vscode from 'vscode';
import * as fs from 'fs';
import * as path from 'path';
declare const WebAssembly: any;

export function activate(context: vscode.ExtensionContext) {
    context.subscriptions.push(vscode.commands.registerCommand('wasmtest.helloWorld', () => {
        const wasm_path = path.join(context.extensionPath, 'media', 'bla.wasm');
        fs.readFile(wasm_path, (err, data) => {
            if (!err) {
                const buf = new Uint8Array(data);
                WebAssembly.instantiate(buf, {}).then((result: any) => {
                    const instance = result.instance;
                    const exports = instance.exports;
                    const res = exports.greeting();
                    const res_ptr = new Uint8Array(exports.memory.buffer, res);
                    let str = "";
                    for (let ii = 0; res_ptr[ii]; ii++) {
                        str += String.fromCharCode(res_ptr[ii]);
                    }
                    vscode.window.showInformationMessage("From WASM: " + str);
                });
            }
        });
    }));
}

export function deactivate() {}