Bug 946390 - Allow content to preventDefault() keypress events targeting <input type=number>. r=smaug

content/html/content/src/HTMLInputElement.cpp

@@ -3835,11 +3835,10 @@ HTMLInputElement::PostHandleEvent(nsEventChainPostVisitor& aVisitor)
       // the editor's handling of up/down keypress events. For that reason we
       // just ignore aVisitor.mEventStatus here and go ahead and handle the
       // event to increase/decrease the value of the number control.
-      // XXX we still need to allow script to call preventDefault() on the
-      // event, but right now we can't tell the difference between the editor
-      // on script doing that (bug 930374).
+      if (!aVisitor.mEvent->mFlags.mDefaultPreventedByContent) {
         StepNumberControlForUserEvent(keyEvent->keyCode == NS_VK_UP ? 1 : -1);
         aVisitor.mEventStatus = nsEventStatus_eConsumeNoDefault;
+      }
     } else if (nsEventStatus_eIgnore == aVisitor.mEventStatus) {
       switch (aVisitor.mEvent->message) {
 

content/html/content/test/forms/test_input_number_key_events.html

@@ -177,6 +177,16 @@ function test() {
     expectedVal = expectedValAfterKeyEvent(key, elem);
     synthesizeKey(key, {});
     is(elem.value, expectedVal, "Test repeat of " + key + " for number control");
+
+    // Test preventDefault():
+    elem.addEventListener("keypress", function(evt) {
+      evt.preventDefault();
+      elem.removeEventListener("keypress", arguments.callee, false);
+    }, false);
+    oldVal = elem.value = 0;
+    expectedVal = 0;
+    synthesizeKey(key, {});
+    is(elem.value, expectedVal, "Test " + key + " for number control where scripted preventDefault() should prevent the value changing");
   }
 }