Implement repr for pyodide/pyscript (#3651)

* Implement repr for pyodide/pyscript

* Generalize

panel/io/pyodide.py

@@ -9,7 +9,9 @@
 
 from bokeh import __version__
 from bokeh.document import Document
+from bokeh.embed.elements import script_for_render_items
 from bokeh.embed.util import standalone_docs_json_and_render_items
+from bokeh.embed.wrappers import wrap_in_script_tag
 from bokeh.io.doc import set_curdoc
 from bokeh.protocol.messages.patch_doc import process_document_events
 from js import JSON
@@ -92,10 +94,48 @@ def pysync(event):
 
     pydoc.on_change(pysync)
 
+async def _link_model(ref, doc):
+    from js import Bokeh
+    rendered = Bokeh.index.object_keys()
+    if ref not in rendered:
+        await asyncio.sleep(0.1)
+        await _link_model(ref, doc)
+        return
+    views = Bokeh.index.object_values()
+    view = views[rendered.indexOf(ref)]
+    _link_docs(doc, view.model.document)
+
 #---------------------------------------------------------------------
 # Public API
 #---------------------------------------------------------------------
 
+def render_script(obj, target):
+    """
+    Generates a script to render the supplied object to the target.
+
+    Arguments
+    ---------
+    obj: Viewable
+        Object to render into the DOM node
+    target: str
+        Target ID of the DOM node to render the object into.
+    """
+    from js import document
+
+    from ..pane import panel as as_panel
+
+    doc = Document()
+    as_panel(obj).server_doc(doc, location=False)
+    docs_json, [render_item,] = standalone_docs_json_and_render_items(
+        doc.roots, suppress_callback_warning=True
+    )
+    for root in doc.roots:
+        render_item.roots._roots[root] = target
+    document.getElementById(target).classList.add('bk-root')
+    script = script_for_render_items(docs_json, [render_item])
+    asyncio.create_task(_link_model(doc.roots[0].ref['id'], doc))
+    return wrap_in_script_tag(script)
+
 def serve(*args, **kwargs):
     """
     Stub to replace Tornado based serve function.

panel/viewable.py

@@ -601,6 +601,14 @@ def __str__(self) -> str:
         return self.__repr__()
 
     def _repr_mimebundle_(self, include=None, exclude=None):
+        if state._is_pyodide:
+            from .io.pyodide import render_script
+            if hasattr(sys.stdout, '_out'):
+                target = sys.stdout._out # type: ignore
+            else:
+                raise ValueError("Could not determine target node to write to.")
+            return {'text/html': render_script(self, target)}, {}
+
         loaded = panel_extension._loaded
         if not loaded and 'holoviews' in sys.modules:
             import holoviews as hv  # type: ignore