Feature: Add hooks for layout "pre" and "post"

CHANGELOG.md

@@ -3,6 +3,13 @@ All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](https://semver.org/).
 
 
+## UNRELEASED
+
+## Added
+
+- [#2630](https://github.com/plotly/dash/pull/2630) New layout hooks in the renderer
+
+
 ## [2.12.1] - 2023-08-16
 
 ## Fixed

dash/_utils.py

@@ -11,7 +11,9 @@
 import secrets
 import string
 from html import escape
-from functools import wraps
+from functools import wraps, reduce
+from typing import Union
+from dash.types import RendererHooks
 
 logger = logging.getLogger()
 
@@ -267,3 +269,15 @@ def coerce_to_list(obj):
 
 def clean_property_name(name: str):
     return name.split("@")[0]
+
+
+def hooks_to_js_object(hooks: Union[RendererHooks, None]) -> str:
+    if hooks is None:
+        return ""
+    hook_str = reduce(
+        lambda reduced, hook: f"{reduced}{hook[0]}: {hook[1]},",
+        hooks.items(),
+        "",
+    )
+
+    return f"{{{hook_str}}}"

dash/dash-renderer/src/APIController.react.js

@@ -123,14 +123,21 @@ function storeEffect(props, events, setErrorLoading) {
         dispatch,
         error,
         graphs,
+        hooks,
         layout,
         layoutRequest
     } = props;
 
     if (isEmpty(layoutRequest)) {
+        if (typeof hooks.layout_pre === 'function') {
+            hooks.layout_pre();
+        }
         dispatch(apiThunk('_dash-layout', 'GET', 'layoutRequest'));
     } else if (layoutRequest.status === STATUS.OK) {
         if (isEmpty(layout)) {
+            if (typeof hooks.layout_post === 'function') {
+                hooks.layout_post(layoutRequest.content);
+            }
             const finalLayout = applyPersistence(
                 layoutRequest.content,
                 dispatch
@@ -190,6 +197,7 @@ UnconnectedContainer.propTypes = {
     dispatch: PropTypes.func,
     dependenciesRequest: PropTypes.object,
     graphs: PropTypes.object,
+    hooks: PropTypes.object,
     layoutRequest: PropTypes.object,
     layout: PropTypes.object,
     loadingMap: PropTypes.any,
@@ -203,6 +211,7 @@ const Container = connect(
     state => ({
         appLifecycle: state.appLifecycle,
         dependenciesRequest: state.dependenciesRequest,
+        hooks: state.hooks,
         layoutRequest: state.layoutRequest,
         layout: state.layout,
         loadingMap: state.loadingMap,

dash/dash-renderer/src/AppContainer.react.js

@@ -13,6 +13,8 @@ class UnconnectedAppContainer extends React.Component {
     constructor(props) {
         super(props);
         if (
+            props.hooks.layout_pre !== null ||
+            props.hooks.layout_post !== null ||
             props.hooks.request_pre !== null ||
             props.hooks.request_post !== null ||
             props.hooks.callback_resolved !== null ||

dash/dash-renderer/src/AppProvider.react.tsx

@@ -16,6 +16,8 @@ const AppProvider = ({hooks}: any) => {
 
 AppProvider.propTypes = {
     hooks: PropTypes.shape({
+        layout_pre: PropTypes.func,
+        layout_post: PropTypes.func,
         request_pre: PropTypes.func,
         request_post: PropTypes.func,
         callback_resolved: PropTypes.func,
@@ -25,6 +27,8 @@ AppProvider.propTypes = {
 
 AppProvider.defaultProps = {
     hooks: {
+        layout_pre: null,
+        layout_post: null,
         request_pre: null,
         request_post: null,
         callback_resolved: null,

dash/dash-renderer/src/reducers/hooks.js

@@ -1,5 +1,7 @@
 const customHooks = (
     state = {
+        layout_pre: null,
+        layout_post: null,
         request_pre: null,
         request_post: null,
         callback_resolved: null,

dash/dash.py

@@ -16,6 +16,7 @@
 import base64
 import traceback
 from urllib.parse import urlparse
+from typing import Union
 
 import flask
 
@@ -52,6 +53,7 @@
     to_json,
     convert_to_AttributeDict,
     gen_salt,
+    hooks_to_js_object,
 )
 from . import _callback
 from . import _get_paths
@@ -70,6 +72,7 @@
     _import_layouts_from_pages,
 )
 from ._jupyter import jupyter_dash, JupyterDisplayMode
+from .types import RendererHooks
 
 # Add explicit mapping for map files
 mimetypes.add_type("application/json", ".map", True)
@@ -134,7 +137,6 @@
 
 
 def _get_traceback(secret, error: Exception):
-
     try:
         # pylint: disable=import-outside-toplevel
         from werkzeug.debug import tbtools
@@ -373,6 +375,7 @@ def __init__(  # pylint: disable=too-many-statements
         long_callback_manager=None,
         background_callback_manager=None,
         add_log_handler=True,
+        hooks: Union[RendererHooks, None] = None,
         **obsolete,
     ):
         _validate.check_obsolete(obsolete)
@@ -466,7 +469,7 @@ def __init__(  # pylint: disable=too-many-statements
         self._favicon = None
 
         # default renderer string
-        self.renderer = "var renderer = new DashRenderer();"
+        self.renderer = f"var renderer = new DashRenderer({hooks_to_js_object(hooks)});"
 
         # static files from the packages
         self.css = Css(serve_locally)
@@ -1301,7 +1304,6 @@ def _setup_server(self):
 
         # Copy over global callback data structures assigned with `dash.callback`
         for k in list(_callback.GLOBAL_CALLBACK_MAP):
-
             if k in self.callback_map:
                 raise DuplicateCallback(
                     f"The callback `{k}` provided with `dash.callback` was already "
@@ -1328,7 +1330,6 @@ def _setup_server(self):
 
         if cancels:
             for cancel_input, manager in cancels.items():
-
                 # pylint: disable=cell-var-from-loop
                 @self.callback(
                     Output(cancel_input.component_id, "id"),
@@ -1719,7 +1720,6 @@ def enable_dev_tools(
             _reload.watch_thread.start()
 
         if debug:
-
             if jupyter_dash.active:
                 jupyter_dash.configure_callback_exception_handling(
                     self, dev_tools.prune_errors
@@ -1753,7 +1753,6 @@ def _after_request(response):
                     dash_total["dur"] = round((time.time() - dash_total["dur"]) * 1000)
 
                 for name, info in timing_information.items():
-
                     value = name
                     if info.get("desc") is not None:
                         value += f';desc="{info["desc"]}"'

dash/types.py

@@ -0,0 +1,10 @@
+from typing_extensions import TypedDict, NotRequired
+
+
+class RendererHooks(TypedDict):
+    layout_pre: NotRequired[str]
+    layout_post: NotRequired[str]
+    request_pre: NotRequired[str]
+    request_post: NotRequired[str]
+    callback_resolved: NotRequired[str]
+    request_refresh_jwt: NotRequired[str]

tests/integration/renderer/test_request_hooks.py

@@ -4,6 +4,7 @@
 import pytest
 
 from dash import Dash, Output, Input, html, dcc
+from dash.types import RendererHooks
 from werkzeug.exceptions import HTTPException
 
 
@@ -115,7 +116,6 @@ def update_output(value):
 
 
 def test_rdrh002_with_custom_renderer_interpolated(dash_duo):
-
     renderer = """
         <script id="_dash-renderer" type="application/javascript">
             console.log('firing up a custom renderer!')
@@ -198,7 +198,6 @@ def update_output(value):
 
 @pytest.mark.parametrize("expiry_code", [401, 400])
 def test_rdrh003_refresh_jwt(expiry_code, dash_duo):
-
     app = Dash(__name__)
 
     app.index_string = """<!DOCTYPE html>
@@ -295,3 +294,31 @@ def wrap(*args, **kwargs):
     dash_duo.wait_for_text_to_equal("#output-token", "..")
 
     assert len(dash_duo.get_logs()) == 2
+
+
+def test_rdrh004_layout_hooks(dash_duo):
+    hooks: RendererHooks = {
+        "layout_pre": """
+            () => {
+                var layoutPre = document.createElement('div');
+                layoutPre.setAttribute('id', 'layout-pre');
+                layoutPre.innerHTML = 'layout_pre generated this text';
+                document.body.appendChild(layoutPre);
+            }
+        """,
+        "layout_post": """
+            (response) => {
+                response.props.children = "layout_post generated this text";
+            }
+        """,
+    }
+
+    app = Dash(__name__, hooks=hooks)
+    app.layout = html.Div(id="layout")
+
+    dash_duo.start_server(app)
+
+    dash_duo.wait_for_text_to_equal("#layout-pre", "layout_pre generated this text")
+    dash_duo.wait_for_text_to_equal("#layout", "layout_post generated this text")
+
+    assert dash_duo.get_logs() == []