Add run_js_blocking to tab API

qutebrowser/browser/browsertab.py

@@ -611,6 +611,14 @@ class AbstractTab(QWidget):
         """
         raise NotImplementedError
 
+    def run_js_blocking(self, code):
+        """Run javascript and block.
+
+        This returns the result to the caller. Its use should be avoided when
+        possible as it runs a local event loop for QtWebEngine.
+        """
+        raise NotImplementedError
+
     def shutdown(self):
         raise NotImplementedError
 

qutebrowser/browser/webengine/webenginetab.py

@@ -343,6 +343,21 @@ class WebEngineTab(browsertab.AbstractTab):
         else:
             self._widget.page().runJavaScript(code, callback)
 
+    def run_js_blocking(self, code):
+        loop = qtutils.EventLoop()
+        js_ret = None
+
+        def js_cb(val):
+            nonlocal js_ret
+            js_ret = val
+            loop.quit()
+
+        self.run_js_async(code, js_cb)
+        loop.exec_()  # blocks until loop.quit() in js_cb
+        assert js_ret is not None
+
+        return js_ret
+
     def shutdown(self):
         log.stub()
 

qutebrowser/browser/webkit/webkittab.py

@@ -525,10 +525,13 @@ class WebKitTab(browsertab.AbstractTab):
             callback(frame.toHtml())
 
     def run_js_async(self, code, callback=None):
-        result = self._widget.page().mainFrame().evaluateJavaScript(code)
+        result = self.run_js_blocking(code)
         if callback is not None:
             callback(result)
 
+    def run_js_blocking(self, code):
+        return self._widget.page().mainFrame().evaluateJavaScript(code)
+
     def icon(self):
         return self._widget.icon()
 

tests/unit/browser/test_tab.py

@@ -121,6 +121,12 @@ def test_tab(qtbot, view, config_stub, tab_registry):
     assert view.parent() is tab_w
 
 
+class TestJs:
+
+    def test_blocking(self, tab):
+        assert tab.run_js_blocking('1 + 1') == 2
+
+
 class TestTabData:
 
     def test_known_attr(self):