Add warning as prevention on drop off of UI from being displayed (gat…

…sbyjs#2614)

* Add console warning as prevention on drop off of UI from being displayed

* Remove console warning from getStateKey as it is not necessary for it is not trying to access the sessionStorage

* Fix linting

* Preserve scroll position in window global when sessionStorage is not available

packages/gatsby-react-router-scroll/src/StateStorage.js

@@ -1,16 +1,41 @@
 const STATE_KEY_PREFIX = `@@scroll|`
+const GATSBY_ROUTER_SCROLL_STATE = `___GATSBY_REACT_ROUTER_SCROLL`
 
 export default class SessionStorage {
   read(location, key) {
     const stateKey = this.getStateKey(location, key)
-    const value = sessionStorage.getItem(stateKey)
-    return JSON.parse(value)
+
+    try {
+      const value = sessionStorage.getItem(stateKey)
+      return JSON.parse(value)
+    } catch (e) {
+      console.warn(`[gatsby-react-router-scroll] Unable to access sessionStorage; sessionStorage is not available.`)
+
+      if (window && window[GATSBY_ROUTER_SCROLL_STATE] && window[GATSBY_ROUTER_SCROLL_STATE][stateKey]) {
+        return window[GATSBY_ROUTER_SCROLL_STATE][stateKey]
+      }
+
+      return ({})
+    }
   }
 
   save(location, key, value) {
     const stateKey = this.getStateKey(location, key)
     const storedValue = JSON.stringify(value)
-    sessionStorage.setItem(stateKey, storedValue)
+
+    try {
+      sessionStorage.setItem(stateKey, storedValue)
+    } catch (e) {
+      if (window && window[GATSBY_ROUTER_SCROLL_STATE]) {
+        window[GATSBY_ROUTER_SCROLL_STATE][stateKey] = JSON.parse(storedValue)
+      } else {
+        window[GATSBY_ROUTER_SCROLL_STATE] = {}
+        window[GATSBY_ROUTER_SCROLL_STATE][stateKey] = JSON.parse(storedValue)
+      }
+
+      console.warn(`[gatsby-react-router-scroll] Unable to save state in sessionStorage; sessionStorage is not available.`)
+    }
+
   }
 
   getStateKey(location, key) {

yarn.lock

@@ -5965,7 +5965,11 @@ is-binary-path@^1.0.0:
   dependencies:
     binary-extensions "^1.0.0"
 
-is-buffer@^1.0.2, is-buffer@^1.1.4, is-buffer@^1.1.5, is-buffer@~1.1.1, is-buffer@~1.1.2, is-buffer@~1.1.5:
+is-buffer@^1.0.2, is-buffer@^1.1.4, is-buffer@~1.1.1, is-buffer@~1.1.2, is-buffer@~1.1.5:
+  version "1.1.6"
+  resolved "https://registry.yarnpkg.com/is-buffer/-/is-buffer-1.1.6.tgz#efaa2ea9daa0d7ab2ea13a97b2b8ad51fefbe8be"
+
+is-buffer@^1.1.5:
   version "1.1.5"
   resolved "https://registry.yarnpkg.com/is-buffer/-/is-buffer-1.1.5.tgz#1f3b26ef613b214b88cbca23cc6c01d87961eecc"
 
@@ -7930,6 +7934,10 @@ mime-db@~1.25.0:
   version "1.25.0"
   resolved "https://registry.yarnpkg.com/mime-db/-/mime-db-1.25.0.tgz#c18dbd7c73a5dbf6f44a024dc0d165a1e7b1c392"
 
+mime-db@~1.30.0:
+  version "1.30.0"
+  resolved "https://registry.yarnpkg.com/mime-db/-/mime-db-1.30.0.tgz#74c643da2dd9d6a45399963465b26d5ca7d71f01"
+
 [email protected]:
   version "2.1.13"
   resolved "https://registry.yarnpkg.com/mime-types/-/mime-types-2.1.13.tgz#e07aaa9c6c6b9a7ca3012c69003ad25a39e92a88"