🐛 fix plotly#1098 : also persist 0, empty string etc

fixes plotly#1098 Persistence does not work for Input components when 0 is entered

Author: eddy-geek

CHANGELOG.md

@@ -2,6 +2,9 @@
 All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## Next
+- [#1142](https://github.com/plotly/dash/pull/1142) [Persistence](https://dash.plot.ly/persistence): Also persist 0, empty string etc
+
 ## [1.9.1] - 2020-02-27
 ### Added
 - [#1133](github.com/plotly/dash/pull/1133) Allow the `compress` config variable to be set with an environment variable with DASH_COMPRESS=FALSE

dash-renderer/src/persistence.js

@@ -319,7 +319,7 @@ export function recordUiEdit(layout, newProps, dispatch) {
 
     forEach(persistedProp => {
         const [propName, propPart] = persistedProp.split('.');
-        if (newProps[propName]) {
+        if (newProps[propName] !== undefined) {
             const storage = getStore(persistence_type, dispatch);
             const {extract} = getTransform(element, propName, propPart);
 

tests/integration/renderer/test_persistence.py

@@ -2,6 +2,8 @@
 import pytest
 import time
 
+from selenium.webdriver.common.keys import Keys
+
 import dash
 from dash.dependencies import Input, Output
 
@@ -401,8 +403,8 @@ def set_out(val):
 
     dash_duo.find_element('#persistence-val').send_keys('2')
     dash_duo.wait_for_text_to_equal('#out', 'a')
-    dash_duo.find_element('#persisted').send_keys('ardvark')
-    dash_duo.wait_for_text_to_equal('#out', 'aardvark')
+    dash_duo.find_element('#persisted').send_keys(Keys.BACK_SPACE)  # persist falsy value
+    dash_duo.wait_for_text_to_equal('#out', '')
 
     # alpaca not saved with falsy persistence
     dash_duo.clear_input('#persistence-val')
@@ -412,7 +414,7 @@ def set_out(val):
     dash_duo.find_element('#persistence-val').send_keys('s')
     dash_duo.wait_for_text_to_equal('#out', 'anchovies')
     dash_duo.find_element('#persistence-val').send_keys('2')
-    dash_duo.wait_for_text_to_equal('#out', 'aardvark')
+    dash_duo.wait_for_text_to_equal('#out', '')
 
 
 def test_rdps011_toggle_persistence2(dash_duo):