code: function fileShouldBeDeleted(key, whitelist) {
    for (var i = 0; i < whitelist.length; i++) {
      var expr = whitelist[i];
      if (expr instanceof RegExp) {
        if (expr.test(key)) {
          return false;
        }
      } else if (typeof expr === 'string') {
        if (expr === key) {
          return false;
        }
      } else {
        throw new Error(
          'whitelist param can only contain regular expressions or strings'
        );
      }
    }
    return true;
  }
docs: init file s3 hash
  @param  {String} key filepath
  @param  {Array} whitelist list of expressions that match against files that should not be deleted
  
  @return {Boolean} shouldDelete whether the file should be deleted or not
  @api private