Add --quiet argument to :jseval.

doc/help/commands.asciidoc

@@ -244,12 +244,15 @@ Toggle the web inspector.
 
 [[jseval]]
 === jseval
-Syntax: +:jseval 'js_code'+
+Syntax: +:jseval [*--quiet*] 'js-code'+
 
 Evaluate a JavaScript string.
 
 ==== positional arguments
-* +'js_code'+: The string to evaluate.
+* +'js-code'+: The string to evaluate.
+
+==== optional arguments
+* +*-q*+, +*--quiet*+: Don't show resulting JS object.
 
 ==== note
 * This command does not split arguments after the last argument and handles quotes literally.

qutebrowser/browser/commands.py

@@ -1566,15 +1566,19 @@ class CommandDispatcher:
 
     @cmdutils.register(instance='command-dispatcher', scope='window',
                        maxsplit=0, no_cmd_split=True)
-    def jseval(self, js_code):
+    def jseval(self, js_code, quiet=False):
         """Evaluate a JavaScript string.
 
         Args:
             js_code: The string to evaluate.
+            quiet: Don't show resulting JS object.
         """
         frame = self._current_widget().page().mainFrame()
         out = frame.evaluateJavaScript(js_code)
 
+        if quiet:
+            return
+
         if out is None:
             # Getting the actual error (if any) seems to be difficult. The
             # error does end up in BrowserPage.javaScriptConsoleMessage(), but