This is a fake. Admins have been notified

AJAX in action ;)

Simple way is to extend your view with this JS:

elgg_extend_view('my_plugin/my_plugin_view', 'my_plugin/my_plugin_js');

where 'my_plugin/my_plugin_js' is a PHP file not JS:

<?php  ?>

<script>
require(['jquery'], function($) {
   //do stuff
})
</script>

You can add JS into your view directly as well.

Thanks @Nikolai

Even I wanted to avoid JS inside php, it worked

You can use JS event on open lightbox:

var Ajax = require('elgg/Ajax');

var ajax = new Ajax();

$(document).on('cbox_open', function() {
    $.ajax({
       url: elgg.get_simplecache_url('my_plugin/my_plugin_js.js'),
       dataType: 'script'
    });
}

Which Elgg version?