No-scheme relative path should be routed to HTTP handler only in browser

src/models.ts

@@ -11,7 +11,7 @@
 /* Original source keras/models.py */
 
 // tslint:disable:max-line-length
-import {doc, io, Scalar, serialization, Tensor} from '@tensorflow/tfjs-core';
+import {doc, ENV, io, Scalar, serialization, Tensor} from '@tensorflow/tfjs-core';
 
 import * as K from './backend/tfjs_backend';
 import {History} from './callbacks';
@@ -201,14 +201,25 @@ export async function loadModelInternal(pathOrIOHandler: string|
                                         io.IOHandler): Promise<Model> {
   if (typeof pathOrIOHandler === 'string') {
     const handlers = io.getLoadHandlers(pathOrIOHandler);
-    if (handlers.length === 0) {
+    if (handlers.length === 0 && ENV.get('IS_BROWSER')) {
       // For backward compatibility: if no load handler can be found,
-      // assume it is a relative http path.
+      // assume it is a relative http path. This applies only to the
+      // browser environment.
       handlers.push(io.browserHTTPRequest(pathOrIOHandler));
-    } else if (handlers.length > 1) {
+    }
+    if (handlers.length > 1) {
       throw new ValueError(
           `Found more than one (${handlers.length}) load handlers for ` +
           `URL '${pathOrIOHandler}'`);
+    } else if (handlers.length === 0) {
+      let errorMsg =
+          `Cannot find any load handlers for path string '${pathOrIOHandler}'.`;
+      if (ENV.get('IS_NODE')) {
+        errorMsg +=
+            ' For Node.js, a URL scheme (e.g., file://, http://, https://)' +
+            'is required.';
+      }
+      throw new ValueError(errorMsg);
     }
     pathOrIOHandler = handlers[0];
   }
@@ -326,8 +337,8 @@ export class Sequential extends Model {
    * ```
    * @param layer Layer instance.
    *
-   * @exception ValueError In case the `layer` argument does not know its input
-   *   shape.
+   * @exception ValueError In case the `layer` argument does not know its
+   * input shape.
    * @exception ValueError In case the `layer` argument has multiple output
    *   tensors, or is already connected somewhere else (forbidden in
    *   `Sequential` models).