Usage
This function runs automatically, so it is not called manually. Is this incorrect?
Examples
Prefetch a resource without this function (for reference).
PHP
<link rel="dns-prefetch preconnect" href="//cdnjs.cloudflare.com" />
Preconnect to a domain with this function
PHP
add_filter('nebula_preconnect', 'my_preconnects');
function my_preconnects($array){
$array[] = '//example.com';
return $array;
}
Additional Notes
DNS-Prefetch: Resolve the DNS only to a domain.
Preconnect: Resolve both DNS and TCP to a domain.
Prefetch: Fully request a single resource and store it in cache until needed.
Prerender: Render an entire page (useful for comment next page navigation). Use Audience > User Flow report in Google Analytics for better predictions.
This function does not use parameters; it relies exclusively on hooks with add_filter() (see examples).
Note: WordPress does add dns-prefetch to all enqueued resource domains automatically.
Source File
Located in /libs/Optimization.php on line 438.
4 Hooks
Find these filters and actions in the source code below to hook into them. Use do_action() and add_filter() in your functions file or plugin.
Filters
"pre_nebula_prebrowsing""nebula_preconnect"
"nebula_prefetches"
"nebula_preloads"
Need a new filter hook? Request one here.
Actions
This function has no action hooks available. Request one?Note: This function contains 13 to-do comments.
PHP
public function prebrowsing(){
$override = apply_filters('pre_nebula_prebrowsing', null);
if ( isset($override) ){return;}
$debug_comment = ( $this->is_dev() )? '<!-- Server-side -->' : '';
/*==========================
DNS-Prefetch & Preconnect
Resolve DNS and TCP to a domain.
===========================*/
$default_preconnects = array();
//Google fonts if used
if ( $this->get_option('remote_font_url') ){
if ( strpos($this->get_option('remote_font_url'), 'google') || strpos($this->get_option('remote_font_url'), 'gstatic') ){ //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
$default_preconnects[] = '//fonts.gstatic.com';
} elseif ( strpos($this->get_option('remote_font_url'), 'typekit') ){ //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
$default_preconnects[] = '//use.typekit.net';
}
}
//Loop through all of the preconnects
$preconnects = apply_filters('nebula_preconnect', $default_preconnects);
if ( !empty($preconnects) && is_array($preconnects) ){
foreach ( $preconnects as $preconnect ){
echo '<link rel="preconnect" href="' . $preconnect . '" crossorigin="anonymous" />' . $debug_comment;
}
}
/*==========================
Prefetch
Fully request a single resource and store it in cache until needed. Do not combine with preload!
===========================*/
$default_prefetches = array();
//Subpages
// if ( !is_front_page() ){
// //$default_prefetches[] = home_url('/'); //Prefetch the home page on subpages. Disabled because this may be loading more than we want on initial pageload
// }
//Search Results
if ( is_search() ){
global $wp_query;
if ( !empty($wp_query->posts) && !empty($wp_query->posts['0']) ){ //If has search results
$default_prefetches[] = get_permalink($wp_query->posts['0']->ID); //Prefetch the first search result
}
}
//404 Pages
if ( is_404() ){
//If Nebula finds a match based on context clues, prefetch that too
if ( !empty($this->error_404_exact_match) ){
$default_prefetches[] = get_permalink($this->error_404_exact_match->ID);
}
//If has page suggestions prefetch the first one
if ( !empty($this->error_query) && $this->error_query->have_posts() ){
$default_prefetches[] = get_permalink($this->error_query->posts[0]->ID);
}
}
//Loop through all of the prefetches
$prefetches = apply_filters('nebula_prefetches', $default_prefetches); //Allow child themes and plugins to prefetch resources via Nebula too
if ( !empty($prefetches) && is_array($prefetches) ){
foreach ( $prefetches as $prefetch ){
echo '<link rel="prefetch" href="' . $prefetch . '" crossorigin="anonymous" />' . $debug_comment;
}
}
/*==========================
Preload
Fully request a single resource before it is needed. Do not combine with prefetch! These must be used within a few seconds of window load.
===========================*/
$default_preloads = array();
//Google fonts if used
/*
if ( $this->get_option('remote_font_url') ){
$default_preloads[] = $this->get_option('remote_font_url'); //Oct 2019: disabling this for now as it delays render in Chrome
}
*/
//Loop through all of the preloads
$preloads = apply_filters('nebula_preloads', $default_preloads); //Allow child themes and plugins to preload resources via Nebula too
if ( !empty($preloads) && is_array($preloads) ){
foreach ( $preloads as $preload ){
switch ( $preload ){
case strpos($preload, '.css'): //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
$filetype = 'style';
break;
case strpos($preload, '.js'): //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
$filetype = 'script';
break;
case strpos($preload, 'fonts.googleapis'): //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
case strpos($preload, '.woff'): //Captures both .woff and .woff2 //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
$filetype = 'font';
break;
case strpos($preload, '.jpg'): //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
case strpos($preload, '.jpeg'): //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
case strpos($preload, '.png'): //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
case strpos($preload, '.gif'): //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
$filetype = 'image';
break;
case strpos($preload, '.mp4'): //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
case strpos($preload, '.ogv'): //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
case strpos($preload, '.mov'): //@todo "Nebula" 0: Update strpos() to str_contains() in PHP8
$filetype = 'video';
break;
default:
$filetype = 'fetch';
break;
}
echo '<link rel="preload" href="' . $preload . '" as="' . $filetype . '" crossorigin="anonymous" />';
}
}
}
Override
To override this PHP function, use this hook in your child theme or plugin ("my_custom" can be changed):
PHP
add_filter('pre_nebula_prebrowsing', 'my_custom_prebrowsing');
function my_custom_prebrowsing(){
//Write your own code here
return true; //Return true to prevent the original function from running afterwords
}
You can completely disable this PHP function with a single line actions:
PHP
add_filter('pre_nebula_prebrowsing', '__return_false');