1. @DomName('WebGL2RenderingContext.isTransformFeedback')
  2. @DocsEditable()
  3. @Experimental()
bool isTransformFeedback(TransformFeedback feedback)

Source 

@DomName('WebGL2RenderingContext.isTransformFeedback')
@DocsEditable()
@Experimental() // untriaged
bool isTransformFeedback(TransformFeedback feedback) =>
    _blink.BlinkWebGL2RenderingContext.instance
        .isTransformFeedback_Callback_1_(this, feedback);