(feat): support SSR out-of-the-box by no-op'ing in Node

- add a `nodeNoop` option that is `true` by default
  - generally folks do not want to hydrate their store during SSR, so
    no-op by default and require explicit opt-in to Node hydration
  - see #6 for discussion
- also throw an Error if localStorage isn't supported and no
  alternative storage provider has been given

(docs): add `nodeNoop` option and section on Node and SSR usage to
give more details and note possible gotchas

README.md

@@ -53,9 +53,17 @@ persist('some', someStore, {
     - **jsonify** *bool* Enables serialization as JSON (default: `true`).
     - **whitelist** *Array\<string\>* Only these keys will be persisted (defaults to all keys).
     - **blacklist** *Array\<string\>* These keys will not be persisted (defaults to all keys).
+    - **nodeNoop** *bool* Whether this should no-op in a Node environment (default: `true`). See below for more details.
 
 - returns a void Promise
 
+### Node and SSR Usage
+
+To support Server-Side Rendering (SSR) out-of-the-box, `persist` will no-op in a Node environment by default.<br>
+Please note that it uses `typeof window === 'undefined'` to check. [`window` is defined in React Native](https://stackoverflow.com/questions/49911424/what-does-the-variable-window-represent-in-react-native), but may not be in test runners and other simulated environments.
+
+If you'd like to hydrate your store in Node (vs. in the browser, which is the standard usage), set `nodeNoop` to `false` and `storage` to a supported provider for Node.
+
 ## Examples
 
 None yet, but can take a look at [agilgur5/react-native-manga-reader-app](https://github.com/agilgur5/react-native-manga-reader-app) which uses it in production.

src/index.ts

@@ -9,16 +9,32 @@ export interface IOptions {
   storage?: any,
   jsonify?: boolean,
   readonly whitelist?: Array<string>,
-  readonly blacklist?: Array<string>
+  readonly blacklist?: Array<string>,
+  nodeNoop?: boolean
 }
 type StrToAnyMap = {[key: string]: any}
 
 export const persist: IArgs = (name, store, options = {}) => {
-  let {storage, jsonify, whitelist, blacklist} = options
+  let {storage, jsonify, whitelist, blacklist, nodeNoop} = options
 
-  if (typeof window.localStorage !== 'undefined' && (!storage || storage === window.localStorage)) {
+  // no-op in node by default to support SSR out-of-the-box
+  // require explicit opt-in to hydrate server-side
+  if (!nodeNoop) { nodeNoop = true }
+  if (nodeNoop && typeof window === 'undefined') { return Promise.resolve() }
+
+  // use AsyncLocalStorage by default or if window.localStorage was passed in
+  if (
+    typeof window !== 'undefined' &&
+    typeof window.localStorage !== 'undefined' &&
+    (!storage || storage === window.localStorage)
+  ) {
     storage = AsyncLocalStorage
   }
+  if (!storage) {
+    return Promise.reject('localStorage (the default) is not supported in ' +
+      'this environment, please configure a supported storage provider')
+  }
+
   if (!jsonify) { jsonify = true } // default to true like mobx-persist
   const whitelistDict = arrToDict(whitelist)
   const blacklistDict = arrToDict(blacklist)