I have seen this example (https://playcanvas.com/editor/project/751877) where the iframe is added to a plane having renderer attached. I am trying to achieve the same with an image. I have changed the code from:
this.entity.renderer.material = material;
to:
this.entity.element.material = material;
but it does not really work. Can anyone help me? I have created an example project here:
https://playcanvas.com/project/849967/overview/test_iframe
It’s not clear to me what you’re trying to do. Are you trying to add the material to the plane? Or do you want the plane to show the iFrame?
I am trying to add iframe in the 2D image. The 2D image has a material right? So how do I display the iframe in it? 
Off hand, I don’t think this iframe method works with 2D screenspace elements because the whole system relies on a 3D world position and orientation.
You would have to create your own iframe ‘plane’ for 2D elements to handle the position, size and rotation of the iframe DOM object.