I'm trying to instantiate a .wasm file locally in node.js. The goal is to run the binary locally and reproduce the functionalities of the web page. Here's my minimum reproducible example:

const fetch = require("node-fetch");

const importObject = {
  imports: {
    imported_func: function(arg) {
      console.log(arg);
    }
  }
};

fetch('.wasm').then(response =>
  response.arrayBuffer()
).then(bytes => {
  let mod = new WebAssembly.Module(bytes);
  let instance = new WebAssembly.Instance(mod, importObject);
  instance.exports.exported_func();
})

The error I get is:

TypeError: WebAssembly.Instance(): Import #0 module="wasi_unstable" error: module is not an object or function

I saw some questions with similar problems but no real solutions were provided. This is my first time working with wasm so I'm pretty lost.

I'm trying to instantiate a .wasm file locally in node.js. The goal is to run the binary locally and reproduce the functionalities of the web page. Here's my minimum reproducible example:

const fetch = require("node-fetch");

const importObject = {
  imports: {
    imported_func: function(arg) {
      console.log(arg);
    }
  }
};

fetch('https://www.supremenewyork./ticket.wasm').then(response =>
  response.arrayBuffer()
).then(bytes => {
  let mod = new WebAssembly.Module(bytes);
  let instance = new WebAssembly.Instance(mod, importObject);
  instance.exports.exported_func();
})

The error I get is:

TypeError: WebAssembly.Instance(): Import #0 module="wasi_unstable" error: module is not an object or function

I saw some questions with similar problems but no real solutions were provided. This is my first time working with wasm so I'm pretty lost.

• javascript
• node.js
• webassembly

3 Answers 3

Your module seems to depend on the wasi_unstable API. If you want to load it you will need an implementation of that API.

To see exactly what imports you module needs you can use wasm2wat or wasmdis tools from wabt and binaryen projects respectively.

If you built your wasm module with emscripten then the remended practice is to have the emscripten generate JS to that implenents these APIs and takes case of loading the module for you.

If you build your wasm module with the wasi-sdk then you need some kind of web polyfill for the WASI APIs.

This will make the error go away:

const importObject = {
  imports: {
    imported_func: function(arg) {
      console.log(arg);
    },
    wasi_unstable: () => {}
  }
};

Try this one

const importObject = {
    wasi_unstable: {
        imported_func: function(args) {
            console.log(args);
        }
    }
};