code: public function getAssetUrl($bundle, $asset)
      {
          if (($actualAsset = $this->resolveAsset($bundle, $asset)) !== false) {
              if (strncmp($actualAsset, '@web/', 5) === 0) {
                  $asset = substr($actualAsset, 5);
                  $basePath = Yii::getAlias('@webroot');
                  $baseUrl = Yii::getAlias('@web');
              } else {
                  $asset = Yii::getAlias($actualAsset);
                  $basePath = $this->basePath;
                  $baseUrl = $this->baseUrl;
              }
          } else {
              $basePath = $bundle->basePath;
              $baseUrl = $bundle->baseUrl;
          }
  
          if (!Url::isRelative($asset) || strncmp($asset, '/', 1) === 0) {
              return $asset;
          }
  
          if ($this->appendTimestamp && ($timestamp = @filemtime("$basePath/$asset")) > 0) {
              return "$baseUrl/$asset?v=$timestamp";
          } else {
              return "$baseUrl/$asset";
          }
      }
docs: Returns the actual URL for the specified asset.
  The actual URL is obtained by prepending either [[baseUrl]] or [[AssetManager::baseUrl]] to the given asset path.
  @param AssetBundle $bundle the asset bundle which the asset file belongs to
  @param string $asset the asset path. This should be one of the assets listed in [[js]] or [[css]].
  @return string the actual URL for the specified asset.