def evaluate(str, file = '<in QML::Engine#evaluate>', lineno = 1)
      evaluate_impl(str, file, lineno).tap do |result|
        raise result.to_error if result.is_a?(JSObject) && result.error?
      end
    end
def evaluate(str, file = '<in QML::Engine#evaluate>', lineno = 1)
      evaluate_impl(str, file, lineno).tap do |result|
        raise result.to_error if result.is_a?(JSObject) && result.error?
      end
    end
Evaluates an JavaScript expression
 @param [String] str The JavaScript string
 @param [String] file The file name
 @param [Integer] lineno The line number