Ensure only one downgrade request is sent per page load, and make the identification of a neccesary downgrade process front-end, not back-end

Author: Clorith

class-jquery-migrate-helper.php

@@ -236,27 +236,6 @@ public static function downgrade_jquery_version() {
  return;
  }
 
-// An array of functions that may trigger a jQuery Migrate downgrade.
-$deprecated = array(
-'andSelf',
- 'browser',
- 'live',
- 'boxModel',
- 'support.boxModel',
- 'size',
- 'swap',
- 'clean',
- 'sub',
-);
-
-preg_match( '/\)\.(?<function>.+?) is not a function/si', $_POST['msg'], $regex_match );
-$function = ( isset( $regex_match['function'] ) ? $regex_match['function'] : null );
-
-// If no function was detected, or it was not an acknowledged deprecated feature, do not downgrade.
-if ( null === $function || ! in_array( $function, $deprecated ) ) {
-return;
-}
-
 update_option( '_jquery_migrate_downgrade_version', 'yes' );
 update_option( '_jquery_migrate_has_auto_downgraded', 'yes' );
 
@@ -282,9 +261,37 @@ public static function fatal_error_handler() {
 ?>
 
  <script type="text/javascript">
+ var jQueryMigrateHelperHasSentDowngrade = false;
+
 window.onerror = function( msg, url, line, col, error ) {
+// Break out early, do not processing if a downgrade reqeust was already sent.
+if ( jQueryMigrateHelperHasSentDowngrade ) {
+return true;
+ }
+
 var xhr = new XMLHttpRequest();
 var nonce = '<?php echo esc_js( wp_create_nonce( 'jquery-migrate-automatic-downgrade' ) ); ?>';
+var jQueryFunctions = [
+'andSelf',
+'browser',
+'live',
+'boxModel',
+'support.boxModel',
+'size',
+'swap',
+'clean',
+'sub',
+ ];
+var match_pattern = /\)\.(.+?) is not a function/;
+ var erroredFunction = msg.match( match_pattern );
+
+ // If there was no matching functions, do not try to downgrade.
+ if ( typeof erroredFunction !== 'object' || typeof erroredFunction[1] === "undefined" || -1 === jQueryFunctions.indexOf( erroredFunction[1] ) ) {
+ return true;
+ }
+
+ // Set that we've now attempted a downgrade request.
+ jQueryMigrateHelperHasSentDowngrade = true;
 
 xhr.open( 'POST', '<?php echo esc_js( admin_url( 'admin-ajax.php' ) ); ?>' );
 xhr.setRequestHeader( 'Content-Type', 'application/x-www-form-urlencoded' );
@@ -308,7 +315,7 @@ public static function fatal_error_handler() {
  }
 };
 
-xhr.send( encodeURI( 'action=jquery-migrate-downgrade-version&_wpnonce=' + nonce + '&msg=' + msg ) );
+xhr.send( encodeURI( 'action=jquery-migrate-downgrade-version&_wpnonce=' + nonce ) );
 
 // Suppress error alerts in older browsers
 return true;