fix: watch didn't work for Vue-only vars

js/src/VueTemplateRenderer.js

@@ -163,27 +163,30 @@ function addModelListeners(model, vueModel) {
 }
 
 function createWatches(model, parentView, templateWatchers) {
-    return model.keys()
-        .filter(prop => !prop.startsWith('_')
-            && !['events', 'template', 'components', 'layout', 'css', 'data', 'methods'].includes(prop))
-        .reduce((result, prop) => ({
-            ...result,
-            [prop]: {
-                handler(value) {
-                    if (templateWatchers && templateWatchers[prop]) {
-                        templateWatchers[prop].bind(this)(value);
-                    }
-                    /* Don't send changes received from backend back */
-                    if (_.isEqual(value, model.get(prop))) {
-                        return;
-                    }
+    const modelWatchers = model.keys().filter(prop => !prop.startsWith('_')
+    && !['events', 'template', 'components', 'layout', 'css', 'data', 'methods'].includes(prop))
+    .reduce((result, prop) => ({
+        ...result,
+        [prop]: {
+            handler(value) {
+                if (templateWatchers && templateWatchers[prop]) {
+                    templateWatchers[prop].bind(this)(value);
+                }
+                /* Don't send changes received from backend back */
+                if (_.isEqual(value, model.get(prop))) {
+                    return;
+                }
 
-                    model.set(prop, value === undefined ? null : _.cloneDeep(value));
-                    model.save_changes(model.callbacks(parentView));
-                },
-                deep: true,
+                model.set(prop, value === undefined ? null : _.cloneDeep(value));
+                model.save_changes(model.callbacks(parentView));
             },
-        }), {});
+            deep: true,
+        },
+    }), {})
+    /* Overwritten keys from templateWatchers are handled in modelWatchers
+        so that we eventually call all handlers from templateWatchers. 
+    */
+    return {...templateWatchers, ...modelWatchers};
 }
 
 function createMethods(model, parentView) {

tests/ui/test_watchers.py

@@ -0,0 +1,94 @@
+import pytest
+import sys
+from playwright.sync_api import Page
+from traitlets import Callable, Int, Unicode, default
+from IPython.display import display
+
+if sys.version_info < (3, 7):
+    pytest.skip("requires python3.7 or higher", allow_module_level=True)
+
+import ipyvue as vue
+
+
+class WatcherTemplateTraitlet(vue.VueTemplate):
+    number = Int(0).tag(sync=True)
+    callback = Callable()
+    text = Unicode("Click Me ").tag(sync=True)
+
+    @default("template")
+    def _default_vue_template(self):
+        return """
+        <template>
+            <div @click="number += 1">{{text + number}}</div>
+        </template>
+        <script>
+        export default {
+            watch: {
+                number: function(value) {
+                    callback();
+                }
+            }
+        }
+        </script>
+        """
+
+    def vue_callback(self):
+        self.callback()
+
+
+# We test that the watcher is activated when a var from python is changed
+def test_watcher_traitlet(solara_test, page_session: Page):
+    def callback():
+        widget.text = "Clicked "
+
+    widget = WatcherTemplateTraitlet(callback=callback)
+
+    display(widget)
+
+    widget = page_session.locator("text=Click Me 0")
+    widget.click()
+    widget = page_session.locator("text=Clicked 1")
+
+
+class WatcherTemplateVue(vue.VueTemplate):
+    callback = Callable()
+    text = Unicode("Click Me ").tag(sync=True)
+
+    @default("template")
+    def _default_vue_template(self):
+        return """
+        <template>
+            <div @click="number += 1">{{text + number}}</div>
+        </template>
+        <script>
+        export default {
+            watch: {
+                number: function(value) {
+                    callback();
+                }
+            },
+            data(){
+                return {
+                    number: 0
+                }
+            }
+        }
+        </script>
+        """
+
+    def vue_callback(self):
+        self.callback()
+
+
+# We test that watch works for a purely Vue variable
+def test_watcher_vue(solara_test, page_session: Page):
+    def callback():
+        widget.text = "Clicked "
+
+    widget = WatcherTemplateVue(callback=callback)
+
+    display(widget)
+
+    widget = page_session.locator("text=Click Me 0")
+    widget.click()
+    widget = page_session.locator("text=Clicked 1")