Everything is being called twice

[luciano_mb]

I noticed the problem when I was setting up an Ajax action which creates a file with a random name. It always created 2 files with random names.

This is a clean install.

I went ahead and started debugging the core files and realized that everything is called twice. For example, try echoing "ok" in the wp() function in wp-includes/functions.php - it will output "okok" in the front-end.

Is this by design or is there something wrong with the current version of WP?
Is there something I should do to avoid this?

Thank you.

Steps to reproduce:

1 - Add this function to the theme functions.php:

function test() {
  fopen("/var/www/html/yourpath/test." . random_int(0, 100000), "w");
  die();
}
add_action('wp_ajax_test', 'test');

2 - Access the URL: /wp-admin/admin-ajax.php?action=test

3 - Check your directory to see 2 different files were created

[SergeyBiryukov]

Hi there, welcome to WordPress Trac! Thanks for the ticket.

For reference, I could not reproduce the issue with the steps provided, only one file was created on my install.

Similar issues are generally caused by browser prefetching, see #12603, #14382, #19018, #20192, #21658, #28797, #32290, #45108. Some browsers automatically load any <link> elements with rel="next" or rel="prefetch".

So it doesn't look like there's a bug here.