Return each facet’s data source in the AJAX response

<?php
// Each facet's source now can be accessed in JavaScript with FWP.settings.facet_sources['your_facet_name']

add_filter( 'facetwp_render_output', function( $output, $params ) {
  $sources = [];

  foreach ( FWP()->facet->facets as $facet_name => $facet_data ) {
    if ( isset ( $facet_data['source'] ) ) {
      $sources[ $facet_name ] = $facet_data['source'];
    }
  }

  $output['settings']['facet_sources'] = $sources;
  return $output;
}, 10, 2 );