class_docstr: Base class for Dask.distributed UI dashboard components.
  
  This class must have two attributes, ``root`` and ``source``, and one
  method ``update``:
  
  *  source: a Bokeh ColumnDataSource
  *  root: a Bokeh Model
  *  update: a method that consumes the messages dictionary found in
             distributed.bokeh.messages
code: def __init__(self):
      self.source = None
      self.root = None
  
file_path: distributed/distributed/dashboard/components/__init__.py
imports: from __future__ import annotations
  import weakref
  from bokeh.core.properties import without_property_validation
label_desc: Use image node_id 1 to create a new DashboardComponent object  with example: obj = DashboardComponent()