- an optional 2nd parameter can be added when calling JS to be called in case of an error

Author: krpatter-intc

eel/__init__.py

@@ -273,10 +273,14 @@ def _process_message(message, ws):
     elif 'return' in message:
         call_id = message['return']
         if call_id in _call_return_callbacks:
-            callback = _call_return_callbacks.pop(call_id)
-            callback(message['value'])
+            callback, error_callback = _call_return_callbacks.pop(call_id)
+            if message['status'] == 'ok':
+                callback(message['value'])
+            elif message['status'] == 'error' and error_callback is not None:
+                error_callback(message['error'], message['stack'])
         else:
             _call_return_values[call_id] = message['value']
+
     else:
         print('Invalid message received: ', message)
 
@@ -321,9 +325,9 @@ def _call_return(call):
     global _js_result_timeout
     call_id = call['call']
 
-    def return_func(callback=None):
+    def return_func(callback=None, error_callback=None):
         if callback is not None:
-            _call_return_callbacks[call_id] = callback
+            _call_return_callbacks[call_id] = (callback, error_callback)
         else:
             for w in range(_js_result_timeout):
                 if call_id in _call_return_values:

eel/eel.js

@@ -131,8 +131,17 @@ eel = {
                 if(message.hasOwnProperty('call') ) {
                     // Python making a function call into us
                     if(message.name in eel._exposed_functions) {
-                        let return_val = eel._exposed_functions[message.name](...message.args);
-                        eel._websocket.send(eel._toJSON({'return': message.call, 'value': return_val}));
+                        try {
+                            let return_val = eel._exposed_functions[message.name](...message.args);
+                            eel._websocket.send(eel._toJSON({'return': message.call, 'status':'ok', 'value': return_val}));
+                        } catch(err) {
+                            debugger
+                            eel._websocket.send(eel._toJSON(
+                                {'return': message.call,
+                                'status':'error',
+                                'error': err.message,
+                                'stack': err.stack}));
+                        }
                     }
                 } else if(message.hasOwnProperty('return')) {
                     // Python returning a value to us

examples/02 - callbacks/callbacks.py

@@ -18,10 +18,21 @@ def py_exception(error):
 def print_num(n):
     print('Got this from Javascript:', n)
 
+
+def print_num_failed(error, stack):
+    print("This is an example of what javascript errors would look like:")
+    print("\tError: ", error)
+    print("\tStack: ", stack)
+
 # Call Javascript function, and pass explicit callback function    
 eel.js_random()(print_num)
 
 # Do the same with an inline callback
 eel.js_random()(lambda n: print('Got this from Javascript:', n))
 
+# Show error handling
+eel.js_with_error()(print_num, print_num_failed)
+
+
 eel.start('callbacks.html', size=(400, 300))
+

examples/02 - callbacks/web/callbacks.html

@@ -10,6 +10,12 @@
         function js_random() {
             return Math.random();
         }
+
+        eel.expose(js_with_error);
+        function js_with_error() {
+            var test = 0;
+            test.something("does not exist");
+        }
 
         function print_num(n) {
             console.log('Got this from Python: ' + n);