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Run WinML from JavaScript (JS bindings)

This guide shows how to run ONNX model inference from Electron using JS bindings for Windows App SDK ML APIs (execution provider discovery via ExecutionProviderCatalog and model download via ModelCatalog) combined with onnxruntime-node for inference — no C# addon required. Inference runs in an Electron utility process so it doesn't block the main process.

Prerequisites

Before starting this guide, make sure you've:

Install ONNX Runtime for Node:

npm install onnxruntime-node@1.24.3

Important

The Windows App Runtime pre-loads its own onnxruntime.dll into child processes. The onnxruntime-node version must match the ORT ABI bundled with your Windows App SDK version. For Windows App SDK 2.x, use onnxruntime-node@1.24.x.

Step 1: Confirm WinML bindings

The Windows App SDK transitively depends on Microsoft.WindowsAppSDK.ML, so the WinML APIs are already in your generated bindings. Verify:

Requires @microsoft/dynwinrt-codegen ≥ 0.1.0-preview.8 — see Get started with Electron for older-project fallbacks.

node -e "console.log(Object.keys(require('#winapp/bindings')).filter(k => k.startsWith('ExecutionProvider')))"

You should see [ 'ExecutionProvider', 'ExecutionProviderCatalog', 'ExecutionProviderReadyState' ].

Step 2: Download the model via Model Catalog (main process)

Use ModelCatalog from JS bindings to download and cache the model locally. The catalog reads a JSON manifest (hosted remotely or locally) that describes available models and their download URLs. After the first download, subsequent runs use the cached copy:

Create src/winml-model.js:

const { ModelCatalog, ModelCatalogSource, Uri } = require('#winapp/bindings');
const fs = require('node:fs');
const path = require('node:path');

// Remote catalog JSON hosted in the WindowsAppSDK-Samples repo
const MODEL_CATALOG_URL =
  'https://raw.githubusercontent.com/microsoft/WindowsAppSDK-Samples/main/Samples/WindowsML/Resources/SqueezeNetModelCatalog.json';

async function downloadModel(modelId, onProgress) {
  const uri = Uri.createUri(MODEL_CATALOG_URL);
  const source = await ModelCatalogSource.createFromUriAsync(uri);
  const catalog = ModelCatalog.createInstance([source]);
  const model = await catalog.findModelAsync(modelId);

  const op = model.getInstanceAsync();
  if (onProgress) {
    op.progress((value) => {
      try { onProgress(value); } catch {}
    });
  }
  const result = await op;

  const instance = result.getInstance();
  if (!instance) return undefined;

  const paths = instance.modelPaths;
  // modelPaths returns directories containing model files
  for (let i = 0; i < paths.size; i++) {
    const dir = paths.getAt(i);
    if (fs.existsSync(dir) && fs.statSync(dir).isDirectory()) {
      const onnx = fs.readdirSync(dir).find((f) => f.endsWith('.onnx'));
      if (onnx) {
        instance.close();
        return path.join(dir, onnx);
      }
    } else if (dir.endsWith('.onnx')) {
      instance.close();
      return dir;
    }
  }
  instance.close();
  return undefined;
}

module.exports = { downloadModel };

Step 3: Discover and ensure execution providers (main process)

Use ExecutionProviderCatalog to list available providers (CPU, DirectML, QNN/NPU) and ensureReadyAsync to download their runtime if needed:

Create src/winml-ep.js:

const { ExecutionProviderCatalog, ExecutionProviderReadyState, ExecutionProviderReadyResultState } = require('#winapp/bindings');

function listProviders() {
  const catalog = ExecutionProviderCatalog.getDefault();
  return catalog.findAllProviders().map((p) => ({
    name: p.name,
    readyState: p.readyState,
    libraryPath: p.libraryPath,
  }));
}

async function ensureProviderReady(providerName, onProgress) {
  const catalog = ExecutionProviderCatalog.getDefault();
  const providers = catalog.findAllProviders();
  const provider = providers.find((p) => p.name === providerName);
  if (!provider) {
    throw new Error(`Execution provider not found: ${providerName}`);
  }

  if (provider.readyState === ExecutionProviderReadyState.Ready) {
    return { name: provider.name, readyState: 'Ready', libraryPath: provider.libraryPath };
  }

  const op = provider.ensureReadyAsync();
  if (onProgress) {
    op.progress((value) => {
      try { onProgress(value); } catch {}
    });
  }
  const result = await op;
  let readyState;
  if (result.status === ExecutionProviderReadyResultState.Success) readyState = 'Ready';
  else if (result.status === ExecutionProviderReadyResultState.Failure) readyState = 'Failed';
  else readyState = 'InProgress';
  return {
    name: provider.name,
    readyState,
    diagnosticText: result.diagnosticText,
    libraryPath: provider.libraryPath,
  };
}

module.exports = { listProviders, ensureProviderReady };

Step 4: Run inference in a utility process

ONNX Runtime session creation and inference are blocking — run them in an Electron utility process to keep the main process responsive.

4.1. Create the worker

Create src/winml-worker.js (this file runs in a utility process):

const { roInitialize } = require('@microsoft/dynwinrt');

// When dynwinrt and onnxruntime-node share the same process, ORT's native
// init can leave the COM apartment uninitialized. Explicitly init MTA first.
roInitialize(1);

const ort = require('onnxruntime-node');

async function runModel(modelPath, inputData, inputShape, ep) {
  const providers = ep === 'dml'
    ? [{ name: 'dml', deviceId: 0 }, 'cpu']
    : ['cpu'];

  const session = await ort.InferenceSession.create(modelPath, {
    executionProviders: providers,
    graphOptimizationLevel: 'all',
  });

  const inputName = session.inputNames[0];
  const input = new ort.Tensor('float32', inputData, inputShape);
  const outputs = await session.run({ [inputName]: input });
  return Array.from(outputs[session.outputNames[0]].data);
}

process.parentPort.on('message', async (e) => {
  const { id, method, args } = e.data;
  try {
    if (method === 'classify') {
      const [modelPath, inputData, inputShape, ep] = args;
      const result = await runModel(modelPath, new Float32Array(inputData), inputShape, ep);
      process.parentPort.postMessage({ id, ok: true, result });
    }
  } catch (err) {
    process.parentPort.postMessage({ id, ok: false, error: err.message });
  }
});

4.2. Launch and call the worker from main

Add the following to your src/index.js:

const { utilityProcess } = require('electron');
const path = require('node:path');
const { listProviders, ensureProviderReady } = require('./winml-ep.js');
const { downloadModel } = require('./winml-model.js');

let worker = null;
let workerReady = null;
const pending = new Map();
let nextId = 1;

function startWinmlWorker() {
  worker = utilityProcess.fork(path.join(__dirname, 'winml-worker.js'), [], {
    stdio: 'pipe',
    serviceName: 'winml-worker',
  });
  worker.on('message', (msg) => {
    const entry = pending.get(msg.id);
    if (!entry) return;
    pending.delete(msg.id);
    if (msg.ok) entry.resolve(msg.result);
    else entry.reject(new Error(msg.error));
  });
  workerReady = new Promise((resolve) => worker.once('spawn', resolve));
}

async function classify(modelPath, inputData, inputShape, ep) {
  if (!worker) startWinmlWorker();
  await workerReady;
  return new Promise((resolve, reject) => {
    const id = nextId++;
    pending.set(id, { resolve, reject });
    worker.postMessage({ id, method: 'classify', args: [modelPath, Array.from(inputData), inputShape, ep] });
  });
}

4.3. Use it

Make sure your createWindow function is async, then add:

const createWindow = async () => {
  // ... existing window creation code ...

  // List and ensure all execution providers are ready
  const providers = listProviders();
  console.log('Available providers:', providers);

  for (const ep of providers) {
    console.log(`Ensuring ${ep.name} is ready...`);
    const result = await ensureProviderReady(ep.name, (progress) => {
      const pct = progress <= 1 ? Math.round(progress * 100) : Math.round(progress);
      process.stdout.write(`\r  ${ep.name}: ${pct}%`);
    });
    process.stdout.write('\n');
    console.log(`  ${ep.name}: ${result.readyState}`);
  }

  // Download model via Model Catalog (cached after first run)
  console.log('Downloading model...');
  const modelPath = await downloadModel('squeezenet', (progress) => {
    if (progress >= 0 && progress <= 100) {
      process.stdout.write(`\rDownloading model: ${Math.round(progress)}%`);
    }
  });
  process.stdout.write('\n');
  console.log('Model path:', modelPath);

  // Run inference in utility process (replace with real preprocessed data)
  const inputData = new Float32Array(1 * 3 * 224 * 224);
  const output = await classify(modelPath, inputData, [1, 3, 224, 224], 'dml');

  console.log('Model output (top 5 values):', output.slice(0, 5));
};

Step 5: Run it

npx winapp node add-electron-debug-identity
npm start

You should see the available execution providers and model output in the console.

Tip

For a complete image-classification pipeline with image decoding via JS bindings (StorageFile, BitmapDecoder, BitmapTransform), see the Electron Gallery WinML sample.

Next Steps

Congratulations! You're running WinML execution providers and ONNX Runtime from JavaScript — no C# addon required. 🎉

Now you're ready to:

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