core/core.libraries.yml                  |  1 +
 core/misc/drupal.js                      | 16 ++++++++++++++++
 core/modules/contextual/js/contextual.js | 10 +++++-----
 core/modules/history/js/history.js       |  5 +++++
 core/modules/quickedit/js/quickedit.js   |  6 +-----
 core/modules/system/system.module        |  7 +++++++
 core/modules/toolbar/js/toolbar.js       |  5 +++++
 sites/development.services.yml           | 13 +++++++++++++
 8 files changed, 53 insertions(+), 10 deletions(-)

diff --git a/core/core.libraries.yml b/core/core.libraries.yml
index 90d3cc3..830e3b5 100644
--- a/core/core.libraries.yml
+++ b/core/core.libraries.yml
@@ -54,6 +54,7 @@ drupalSettings:
   version: VERSION
   drupalSettings:
     # These placeholder values will be set by system_js_settings_alter().
+    clientSideCaching: true
     path:
       baseUrl: null
       scriptPath: null
diff --git a/core/misc/drupal.js b/core/misc/drupal.js
index dcfad00..70a9356 100644
--- a/core/misc/drupal.js
+++ b/core/misc/drupal.js
@@ -428,4 +428,20 @@ if (window.jQuery) {
     return '<em class="placeholder">' + Drupal.checkPlain(str) + '</em>';
   };
 
+  /**
+   * Deletes either from localStorage or sessionStorage by prefix.
+   *
+   * @param Storage storage
+   *   Either window.localStorage or window.sessionStorage
+   * @param String prefix
+   *   The prefix to use to determine which key-value pairs to delete.
+   */
+  Drupal.deleteFromClientSideCacheByPrefix = function(storage, prefix) {
+    Object.keys(storage).forEach(function (key) {
+      if (key.substring(0, prefix.length) === prefix) {
+        storage.removeItem(key);
+      }
+    });
+  };
+
 })(domready, Drupal, window.drupalSettings);
diff --git a/core/modules/contextual/js/contextual.js b/core/modules/contextual/js/contextual.js
index 505b2a8..42debee 100644
--- a/core/modules/contextual/js/contextual.js
+++ b/core/modules/contextual/js/contextual.js
@@ -23,11 +23,7 @@
   var permissionsHash = drupalSettings.user.permissionsHash;
   if (cachedPermissionsHash !== permissionsHash) {
     if (typeof permissionsHash === 'string') {
-      _.chain(storage).keys().each(function (key) {
-        if (key.substring(0, 18) === 'Drupal.contextual.') {
-          storage.removeItem(key);
-        }
-      });
+      Drupal.deleteFromClientSideCacheByPrefix(storage, 'Drupal.contextual.');
     }
     storage.setItem('Drupal.contextual.permissionsHash', permissionsHash);
   }
@@ -157,6 +153,10 @@
 
       // Update all contextual links placeholders whose HTML is cached.
       var uncachedIDs = _.filter(ids, function initIfCached(contextualID) {
+        // Return early if client-side caching is disabled.
+        if (!drupalSettings.clientSideCaching) {
+          return true;
+        }
         var html = storage.getItem('Drupal.contextual.' + contextualID);
         if (html !== null) {
           // Initialize after the current executation cycle, to make the AJAX
diff --git a/core/modules/history/js/history.js b/core/modules/history/js/history.js
index c598dd4..61a0420 100644
--- a/core/modules/history/js/history.js
+++ b/core/modules/history/js/history.js
@@ -19,6 +19,11 @@
     embeddedLastReadTimestamps = drupalSettings.history.lastReadTimestamps;
   }
 
+  // If client-side caching is disabled, remove existing cache items.
+  if (!drupalSettings.clientSideCaching) {
+    Drupal.deleteFromClientSideCacheByPrefix(storage, 'Drupal.history.');
+  }
+
   Drupal.history = {
 
     /**
diff --git a/core/modules/quickedit/js/quickedit.js b/core/modules/quickedit/js/quickedit.js
index d722bea..ebb9c97 100644
--- a/core/modules/quickedit/js/quickedit.js
+++ b/core/modules/quickedit/js/quickedit.js
@@ -164,11 +164,7 @@
   var permissionsHash = drupalSettings.user.permissionsHash;
   if (permissionsHashValue !== permissionsHash) {
     if (typeof permissionsHash === 'string') {
-      _.chain(storage).keys().each(function (key) {
-        if (key.substring(0, 26) === 'Drupal.quickedit.metadata.') {
-          storage.removeItem(key);
-        }
-      });
+      Drupal.deleteFromClientSideCacheByPrefix(storage, 'Drupal.quickedit.metadata.');
     }
     storage.setItem(permissionsHashKey, permissionsHash);
   }
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 8f2a8ab..262067e 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -657,6 +657,13 @@ function system_js_settings_alter(&$settings) {
   if (!isset($settings['locale']['pluralDelimiter'])) {
     $settings['locale']['pluralDelimiter'] = LOCALE_PLURAL_DELIMITER;
   }
+
+  // Allow a 'clientSideCaching' container parameter to override the default
+  // drupalSettings.clientSideCaching = true setting.
+  $container = \Drupal::getContainer();
+  if ($container->hasParameter('clientSideCaching')) {
+    $settings['clientSideCaching'] = $container->getParameter('clientSideCaching');
+  }
 }
 
 /**
diff --git a/core/modules/toolbar/js/toolbar.js b/core/modules/toolbar/js/toolbar.js
index e5b244c..c4f84b9 100644
--- a/core/modules/toolbar/js/toolbar.js
+++ b/core/modules/toolbar/js/toolbar.js
@@ -26,6 +26,11 @@
     }
   );
 
+  // If client-side caching is disabled, remove the cached subtree and its hash.
+  if (!drupalSettings.clientSideCaching) {
+    Drupal.deleteFromClientSideCacheByPrefix(localStorage, 'Drupal.toolbar.subtrees');
+  }
+
   /**
    * Registers tabs with the toolbar.
    *
diff --git a/sites/development.services.yml b/sites/development.services.yml
index cc21211..5a60687 100644
--- a/sites/development.services.yml
+++ b/sites/development.services.yml
@@ -7,3 +7,16 @@ services:
     class: Drupal\Core\Cache\MemoryBackendFactory
   cache.backend.null:
     class: Drupal\Core\Cache\NullBackendFactory
+
+parameters:
+  # Client-side caching.
+  #
+  # By default, client-side caching (e.g. in localStorage and sessionStorage) is
+  # enabled. While developing, you may want to disable this.
+  #
+  # Note: JavaScript code can disable its client-side caching by checking if
+  # drupalSettings.clientSideCaching === false.
+  #
+  # Not recommended in production environments
+  # @default true
+  clientSideCaching: false