diff --git a/components/dash-core-components/src/fragments/DatePickerRange.react.js b/components/dash-core-components/src/fragments/DatePickerRange.react.js
index b548a01148..fe8fab4cc8 100644
--- a/components/dash-core-components/src/fragments/DatePickerRange.react.js
+++ b/components/dash-core-components/src/fragments/DatePickerRange.react.js
@@ -3,7 +3,7 @@ import {DateRangePicker} from 'react-dates';
 import React, {Component} from 'react';
 import uniqid from 'uniqid';
 
-import {propTypes, defaultProps} from '../components/DatePickerRange.react';
+import {propTypes} from '../components/DatePickerRange.react';
 import convertToMoment from '../utils/convertToMoment';
 import LoadingElement from '../utils/LoadingElement';
 
@@ -219,4 +219,3 @@ export default class DatePickerRange extends Component {
 }
 
 DatePickerRange.propTypes = propTypes;
-DatePickerRange.defaultProps = defaultProps;
diff --git a/components/dash-core-components/src/fragments/DatePickerSingle.react.js b/components/dash-core-components/src/fragments/DatePickerSingle.react.js
index 5b5ac3784b..8cbe792588 100644
--- a/components/dash-core-components/src/fragments/DatePickerSingle.react.js
+++ b/components/dash-core-components/src/fragments/DatePickerSingle.react.js
@@ -4,7 +4,7 @@ import {SingleDatePicker} from 'react-dates';
 import moment from 'moment';
 import React, {Component} from 'react';
 
-import {propTypes, defaultProps} from '../components/DatePickerSingle.react';
+import {propTypes} from '../components/DatePickerSingle.react';
 import convertToMoment from '../utils/convertToMoment';
 import LoadingElement from '../utils/LoadingElement';
 
@@ -155,4 +155,3 @@ export default class DatePickerSingle extends Component {
 }
 
 DatePickerSingle.propTypes = propTypes;
-DatePickerSingle.defaultProps = defaultProps;
diff --git a/components/dash-core-components/src/fragments/Markdown.react.js b/components/dash-core-components/src/fragments/Markdown.react.js
index b209c73a7a..557ed863fd 100644
--- a/components/dash-core-components/src/fragments/Markdown.react.js
+++ b/components/dash-core-components/src/fragments/Markdown.react.js
@@ -6,7 +6,7 @@ import RemarkMath from 'remark-math';
 
 import Math from './Math.react';
 import MarkdownHighlighter from '../utils/MarkdownHighlighter';
-import {propTypes, defaultProps} from '../components/Markdown.react';
+import {propTypes} from '../components/Markdown.react';
 
 import DccLink from './../components/Link.react';
 import LoadingElement from '../utils/LoadingElement';
@@ -187,4 +187,3 @@ export default class DashMarkdown extends Component {
 }
 
 DashMarkdown.propTypes = propTypes;
-DashMarkdown.defaultProps = defaultProps;
diff --git a/components/dash-core-components/src/fragments/RangeSlider.react.js b/components/dash-core-components/src/fragments/RangeSlider.react.js
index 4673d2b5df..e0aa0dc312 100644
--- a/components/dash-core-components/src/fragments/RangeSlider.react.js
+++ b/components/dash-core-components/src/fragments/RangeSlider.react.js
@@ -10,7 +10,7 @@ import {
     calcStep,
     setUndefined,
 } from '../utils/computeSliderMarkers';
-import {propTypes, defaultProps} from '../components/RangeSlider.react';
+import {propTypes} from '../components/RangeSlider.react';
 import {
     formatSliderTooltip,
     transformSliderTooltip,
@@ -152,4 +152,3 @@ export default class RangeSlider extends Component {
 }
 
 RangeSlider.propTypes = propTypes;
-RangeSlider.defaultProps = defaultProps;
diff --git a/components/dash-core-components/src/fragments/Slider.react.js b/components/dash-core-components/src/fragments/Slider.react.js
index 61e3d97317..eeebde563d 100644
--- a/components/dash-core-components/src/fragments/Slider.react.js
+++ b/components/dash-core-components/src/fragments/Slider.react.js
@@ -10,7 +10,7 @@ import {
     calcStep,
     setUndefined,
 } from '../utils/computeSliderMarkers';
-import {propTypes, defaultProps} from '../components/Slider.react';
+import {propTypes} from '../components/Slider.react';
 import {
     formatSliderTooltip,
     transformSliderTooltip,
@@ -152,4 +152,3 @@ export default class Slider extends Component {
 }
 
 Slider.propTypes = propTypes;
-Slider.defaultProps = defaultProps;
diff --git a/components/dash-core-components/src/fragments/Upload.react.js b/components/dash-core-components/src/fragments/Upload.react.js
index f106ce99b0..3e9ac0bd34 100644
--- a/components/dash-core-components/src/fragments/Upload.react.js
+++ b/components/dash-core-components/src/fragments/Upload.react.js
@@ -1,7 +1,7 @@
 import React, {Component} from 'react';
 import Dropzone from 'react-dropzone';
 
-import {propTypes, defaultProps} from '../components/Upload.react';
+import {propTypes} from '../components/Upload.react';
 import LoadingElement from '../utils/LoadingElement';
 
 export default class Upload extends Component {
@@ -91,4 +91,3 @@ export default class Upload extends Component {
 }
 
 Upload.propTypes = propTypes;
-Upload.defaultProps = defaultProps;
diff --git a/components/dash-core-components/tests/integration/graph/test_graph_varia.py b/components/dash-core-components/tests/integration/graph/test_graph_varia.py
index 373aa1fee4..582c211aa7 100644
--- a/components/dash-core-components/tests/integration/graph/test_graph_varia.py
+++ b/components/dash-core-components/tests/integration/graph/test_graph_varia.py
@@ -15,6 +15,8 @@
 from selenium.webdriver.support.ui import WebDriverWait
 from selenium.webdriver.support import expected_conditions as EC
 
+from flaky import flaky
+
 
 @pytest.mark.parametrize("is_eager", [True, False])
 def test_grva001_candlestick(dash_dcc, is_eager):
@@ -681,6 +683,7 @@ def load_chart(n_clicks):
     assert dash_dcc.get_logs() == []
 
 
+@flaky(max_runs=3)
 def test_grva008_shapes_not_lost(dash_dcc):
     # See issue #879 and pr #905
     app = Dash(__name__)
diff --git a/components/dash-table/tests/selenium/test_navigation.py b/components/dash-table/tests/selenium/test_navigation.py
index 44e6c1fe09..78c587d5e3 100644
--- a/components/dash-table/tests/selenium/test_navigation.py
+++ b/components/dash-table/tests/selenium/test_navigation.py
@@ -6,6 +6,7 @@
 from selenium.webdriver.common.keys import Keys
 
 import pytest
+import flaky
 
 DATA_SIZE = 50
 
@@ -154,6 +155,7 @@ def test_navg002_keyboard_after_ctrl_copy(test, props):
     assert test.get_log_errors() == []
 
 
+@flaky.flaky(max_runs=3)
 @pytest.mark.parametrize("props", [get_markdown_table(), get_mixed_markdown_table()])
 @pytest.mark.parametrize(
     "key,row,col",
diff --git a/dash/__init__.py b/dash/__init__.py
index 2c8542a6b5..92d9e45a12 100644
--- a/dash/__init__.py
+++ b/dash/__init__.py
@@ -61,6 +61,7 @@ def _jupyter_nbextension_paths():
     "Input",
     "Output",
     "State",
+    "clientside_callback",
     "ClientsideFunction",
     "MATCH",
     "ALLSMALLER",
@@ -88,4 +89,5 @@ def _jupyter_nbextension_paths():
     "Patch",
     "jupyter_dash",
     "ctx",
+    "hooks",
 ]
diff --git a/dash/_callback.py b/dash/_callback.py
index d9bae3d6ec..eb023ea1a3 100644
--- a/dash/_callback.py
+++ b/dash/_callback.py
@@ -68,10 +68,10 @@ def callback(
     *_args,
     background: bool = False,
     interval: int = 1000,
-    progress: Optional[Output] = None,
+    progress: Optional[Union[List[Output], Output]] = None,
     progress_default: Any = None,
     running: Optional[List[Tuple[Output, Any, Any]]] = None,
-    cancel: Optional[List[Input]] = None,
+    cancel: Optional[Union[List[Input], Input]] = None,
     manager: Optional[BaseBackgroundCallbackManager] = None,
     cache_args_to_ignore: Optional[list] = None,
     on_error: Optional[Callable[[Exception], Any]] = None,
diff --git a/tests/integration/multi_page/test_pages_relative_path.py b/tests/integration/multi_page/test_pages_relative_path.py
index 3d6345a4a8..6c505ac3f5 100644
--- a/tests/integration/multi_page/test_pages_relative_path.py
+++ b/tests/integration/multi_page/test_pages_relative_path.py
@@ -50,7 +50,11 @@ def test_pare001_relative_path(dash_duo, clear_pages_state):
     for page in dash.page_registry.values():
         dash_duo.find_element("#" + page["id"]).click()
         dash_duo.wait_for_text_to_equal("#text_" + page["id"], "text for " + page["id"])
-        assert dash_duo.driver.title == page["title"], "check that page title updates"
+        dash_duo._wait_for(
+            lambda _: dash_duo.driver.title == page["title"],
+            msg="check that page title updates",
+            timeout=3,
+        )
 
     assert dash_duo.get_logs() == [], "browser console should contain no error"