code: func (c *Context) GetContextAttributes() ContextAttributes {
  	ca := c.Call("getContextAttributes")
  	return ContextAttributes{
  		ca.Get("alpha").Bool(),
  		ca.Get("depth").Bool(),
  		ca.Get("stencil").Bool(),
  		ca.Get("antialias").Bool(),
  		ca.Get("premultipliedAlpha").Bool(),
  		ca.Get("preservedDrawingBuffer").Bool(),
  	}
  }
docs: // Returns the context attributes active on the context. These values might
  // be different than what was requested on context creation if the
  // browser's implementation doesn't support a feature.