Bug 787102 - (1/2) - Dispatch the change event for input elements even if .value is set while focused. r=bz

content/html/content/src/nsHTMLInputElement.cpp

@@ -1060,9 +1060,24 @@ nsHTMLInputElement::SetValue(const nsAString& aValue)
     }
   }
   else {
-    SetValueInternal(aValue, false, true);
     if (IsSingleLineTextControl(false)) {
-      GetValueInternal(mFocusedValue);
+      // If the value has been set by a script, we basically want to keep the
+      // current change event state. If the element is ready to fire a change
+      // event, we should keep it that way. Otherwise, we should make sure the
+      // element will not fire any event because of the script interaction.
+      //
+      // NOTE: this is currently quite expensive work (too much string
+      // manipulation). We should probably optimize that.
+      nsAutoString currentValue;
+      GetValueInternal(currentValue);
+
+      SetValueInternal(aValue, false, true);
+
+      if (mFocusedValue.Equals(currentValue)) {
+        GetValueInternal(mFocusedValue);
+      }
+    } else {
+      SetValueInternal(aValue, false, true);
     }
   }
 

content/html/content/test/forms/test_change_event.html

@@ -106,6 +106,19 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=722599
     input.blur();
     is(textInputChange[0], 2, "text input element should have dispatched change event (2).");
 
+    // value being set while focused
+    input.focus();
+    input.value = 'foo';
+    input.blur();
+    is(textInputChange[0], 2, "text input element should not have dispatched change event (2).");
+
+    // value being set while focused after being modified manually
+    input.focus();
+    synthesizeKey("f", {});
+    input.value = 'bar';
+    input.blur();
+    is(textInputChange[0], 3, "text input element should not have dispatched change event (3).");
+
     //focus and blur textarea
     var textarea = document.getElementById("textarea");
     textarea.focus();