Add 'Exposed Runtime' to api mappings

- Add global variable to check if `IS_EXPOSED_RUNTIME_ENV` -> true if Js
exposes their own custom runtime.
- Applying 'auto' device as default for exposed runtime environment.

src/backends/onnx.js

@@ -59,11 +59,11 @@ const supportedDevices = [];
 /** @type {ONNXExecutionProviders[]} */
 let defaultDevices;
 let ONNX;
-const ORT_SYMBOL = Symbol.for('onnxruntime');
 
-if (ORT_SYMBOL in globalThis) {
-  // If the JS runtime exposes their own ONNX runtime, use it
-  ONNX = globalThis[ORT_SYMBOL];
+if (apis.IS_EXPOSED_RUNTIME_ENV) {
+    // If the JS runtime exposes their own ONNX runtime, use it
+    ONNX = globalThis[apis.EXPOSED_RUNTIME_SYMBOL];
+    defaultDevices = ['auto'];
 
 } else if (apis.IS_NODE_ENV) {
     ONNX = ONNX_NODE.default ?? ONNX_NODE;

src/env.js

@@ -35,6 +35,9 @@ const IS_WEB_CACHE_AVAILABLE = IS_BROWSER_ENV && 'caches' in self;
 const IS_WEBGPU_AVAILABLE = typeof navigator !== 'undefined' && 'gpu' in navigator;
 const IS_WEBNN_AVAILABLE = typeof navigator !== 'undefined' && 'ml' in navigator;
 
+const EXPOSED_RUNTIME_SYMBOL = Symbol.for('onnxruntime');
+const IS_EXPOSED_RUNTIME_ENV = EXPOSED_RUNTIME_SYMBOL in globalThis;
+
 const IS_PROCESS_AVAILABLE = typeof process !== 'undefined';
 const IS_NODE_ENV = IS_PROCESS_AVAILABLE && process?.release?.name === 'node';
 const IS_FS_AVAILABLE = !isEmpty(fs);
@@ -59,6 +62,12 @@ export const apis = Object.freeze({
     /** Whether the WebNN API is available */
     IS_WEBNN_AVAILABLE,
 
+    /** Symbol from JS environment that exposes their own ONNX runtime */
+    EXPOSED_RUNTIME_SYMBOL,
+
+    /** Whether we are running in a JS environment that exposes their own ONNX runtime */
+    IS_EXPOSED_RUNTIME_ENV,
+
     /** Whether the Node.js process API is available */
     IS_PROCESS_AVAILABLE,
 

src/models.js

@@ -166,7 +166,10 @@ async function getSession(pretrained_model_name_or_path, fileName, options) {
 
     // If the device is not specified, we use the default (supported) execution providers.
     const selectedDevice = /** @type {import("./utils/devices.js").DeviceType} */(
-        device ?? (apis.IS_NODE_ENV ? 'cpu' : 'wasm')
+        device ?? (
+          apis.IS_EXPOSED_RUNTIME_ENV ? 'auto' : (
+            apis.IS_NODE_ENV ? 'cpu' : 'wasm'
+        ))
     );
     const executionProviders = deviceToExecutionProviders(selectedDevice);