https://stackoverflow.com/questions/20484738/submit-form-on-enter-key-with-javascript

Check this permission in /action/comment/add to return false if user will comment on a photo again.

You can use AJAX for this.

In UI use JS to hide comment form after adding a comment to a photo.

Maybe, you need to create a view/json for this page if you're trying to fetch JSON data.

Look at responses when you load your popup (tab 'Network' in browser's DevTools).

Also, are you use json_decode() in your popup?

Perhaps, example of your summary_view could help to understand more...

@RvR,

I think his original question is this: why does Elgg assume that the output of an ajax view is in JSON format?  The view that he is trying to pop up in a lightbox is not JSON, it's just HTML.  But Elgg's AJAX code is treating the view output as though it's JSON, and it fails when trying to call parseJSON() on the view output.

It can be a bit tricky to get lightbox popups working correctly.

First thing is you should register the view to be displayed in the popup as ajax view, e.g. in the init function of your plugin in start.php add the line

elgg_register_ajax_view('plugin_name/summary_view');

with summary_view.php saved at mod/plugin_name/views/default/plugin_name/summary_view.

Then the link would be displayed with (omitted the additional options just for laziness)

echo elgg_view('output/url', array(
    'href' => "ajax/view/plugin_name/summary_view",
    'class' => 'elgg-lightbox',
    'text' => 'Summary',
));

By not registering the view to be displayed as ajax view I'm not sure if lightbox.js and lightbox.css are really loaded correctly (in the past you had to load them on your own when needed but now this should work automatically). And only with the ajax view Elgg might set content type to html. Otherwise it might be undefined (at least I don't see any json output option for content type in the available options at https://www.jacklmoore.com/colorbox/).