Autopreview triggers only on second change (Regression after #13298)

[Cinc-th]

The change in #13298 causes the following regression.

When using the autoSubmit() function in a custom script on the newticket page (see file refresh_actions.js in ​th:wiki/MultipleWorkflowPlugin) a request is only sent on second change of the select control with the attached autoSubmit handler.

This is because

• on the first change the variable values is null and will be initialized in trigger() with the current form data (this is after the change already happened)

      // Trigger a request after the given timeout
     function trigger() {
       if (values === null)
         values = form.serializeArray();
         ...    
     }
  

• in request() called after the timeout the form is again serialized into variable new_values
• comparison of values and new_values yields no difference thus no request is sent.

The newticket page afaics currently works only by chance:

• Because the input control #field-summary has class trac-autofocus it will be activated on load.
• This means another control is losing focus
• The blur event is sent causing the function trigger() to be called and the variable values gets initialized before any change made by the user.

You may test this by removing the class trac-autofocus in ticket.html. Afterwards any first change to any select control will have no effect.

There is a workaround (see below) for plugin developers. Sorry, I don't have a solution right now for the problem.

Workaround

To solve the issue in the plugin I just send the blur event to the element with the attached autoSubmit() handler so values is properly initialized prior to any user input.

jQuery(document).ready(function(){
    $("#field-type").autoSubmit({mw_refresh: '1', preview: '1'}, function(data, reply) {

        [...]

    }, "#action .trac-loading");
    $("#field-type").blur()
});

[Jun Omae]

I don't consider that the plugin should use $("#field-type").autoSubmit() because autoSubmit() doesn't fire when [trac] auto_preview_timeout option or auto-preview timeout in user preferences is 0.

Instead, $("#field-type").on('click', ...) should be used.

[Ryan J Ollos]

I agree with comment:1. autoSubmit isn't good for the use-case.

If the issue arises for appropriate use-cases of autoSubmit we could trigger on the focus event:

trac/htdocs/js/auto_preview.js

@@ -95 +95 @@
     }
 
     // See #11510
-    return inputs.on('input cut paste keydown keypress change blur', trigger);
+    return inputs.on('input cut paste keydown keypress change blur focus', trigger);
   };
 
   // Enable automatic previewing to <textarea> elements.

The values would be initialized on focus, and the change event will fire if the selection is changed.

[Ryan J Ollos]

Moving to 1.4.3 to consider comment:2 change.

[Cinc-th]

I tested the change from comment:2 with Trac 1.4.2.

It fixes the problem for the newticket page. Preview now properly works when CSS class trac-autofocus is not applied to any control.

comment:1 raises valid concerns. I'll revisit the plugin to address the problems.

[Ryan J Ollos]

Fixed in r17465, merged in [17466:17467].