storage-engine

storage-engine

The storage-engine module is an high level abstraction for React-Native's AsyncStorage. It allows you to easily customize the AsyncStorage using plugins. These plugins can be applied to all keys, or just specific key patterns giving you immense flexibility in the storage layer that you're creating.

Installation

The package is released in the public npm registry and can be installed by running:

npm install --save storage-engine

The AsyncStorage API has been moved to the React-Native Community as part of their lean-core initiative and should now be installed as separate package:

npm install --save @react-native-community/async-storage
react-native link @react-native-community/async-storage

Table of Contents

• Installation
• Usage
  • before
  • after
  • plugin
    • Plugin API
  • destroy
  • api
  • getItem
  • setItem
  • removeItem
  • mergeItem
  • clear
  • getAllKeys
  • flushGetRequests
  • multiGet
  • multiSet
  • multiMerge
  • multiRemove
• Debugging
• License

Usage

import storage, { StorageEngine } from 'storage-engine';

We export a pre-initialized StorageEngine class by default so you can use the API directly when you import the module. If you wish, you can create your own instance by initializing a new StorageEngine class.

The storage instance has the following methods:

• before
• after
• plugin
• destroy
• api

Enhanced AsyncStorage methods:

• getItem
• setItem
• removeItem
• mergeItem
• clear
• getAllKeys
• flushGetRequests
• multiGet
• multiSet
• multiMerge
• multiRemove

before

The before method allows you to pre-process any AsyncStorage API call. You can intercept the request, change values, or even change keys. Want to merge data with an remote data source? We gotchu, want to cancel a request, hell yeah.

import storage from 'storage-engine';

storage.before('key*, another, more*', {
  setItem: function ({ key, value, method }) {
    console.log(method);  // setItem
    console.log(key);     // key-here
    console.log(value);   // bar

    return {
      value: 'Completely different value'
    }
  }
});

storage.after('*', {
  setItem: function ({ key, value, method }) {
    console.log(method);  // setItem
    console.log(key);     // key-here
    console.log(value);   // Completely different value
  },
  getItem: function ({ key, value, method }) {
    console.log(method);  // getItem
    console.log(key);     // key-here
    console.log(value);   // undefined
  }
})

await storage.setItem('key-here', 'bar');
const value = await storage.getItem('key-here');

console.log(value);   // Completely different value

In the example above, we've added a before hook that is triggered when the setItem api is called. We can see which key is used, and which value would be assigned. We've then returned a completely different value from the hook which would be stored instead of the original provided value.

The before method accepts the following arguments:

• key A pattern of keys that would need to trigger the assigned before method. It can be key1, key1, another-key or use the * wildcard for all keys, or even a combination key*, another-key, *bar, which would match key1, key0afaf, another-key, foobar, bbar etc.
• methods An object where the key's are the names of the methods you would like to pre-process, and the value the (async)function that would handle the pre-processing. If you supply a (async)function instead of an object, it would be called for all available methods.

After

Exactly the same interface as before, but instead of pre processing this method allows you to post process the response of the AsyncStorage API call.

See before for API and example.

plugin

The plugin API allows you to load any custom plugin that can enhance your storage instance. A plugin is basically an (async) function that is executed with a bunch of plugin helper functions.

import storage from 'storage-engine';
import { expire } from 'storage-modifiers';

storage.use('token*', expire, {
  duration: '30 minutes'
});

storage.use('pattern*', async function example(plugin) {
  const { before, after, destroy, options } = plugin;

  //
  // Main difference here is that plugins don't need to prefix before and
  // after functions with the pattern, this is done automatically.
  //
  before({
    getItem: () => {}
  });

  destroy(function () {
    //
    // Called when `storage.destroy()` is invoked.
    //
  });

  console.log(options); // { options: 'here'}
}, {
  options: 'here'
});

The plugin API accepts the following arguments:

• pattern The key pattern that it should be triggered on.
• plugin The actual plugin which can be an async or normal JavaScript function that will be executed with our Plugin API.
• options Additional options for the plugin.

Please note, we do offer default plugins which are available in a separate module, storage-modifiers which provides useful features such as:

• json: Automatic encoding, and decoding of values
• emit: Emits an event when a given key, or method is accessed (configurable)
• expire: Expires key/values based on a given TTL
• encrypt: Adds an additional layer of protection by encrypting the data you store.

Plugin API

When the plugin is executed by the plugin it will be executed with an object that contains the following properties and helper functions.

• before Reference to the before method, but prefixed by default with the pattern that was supplied to the plugin.
• after Reference to the after method, but prefixed by default with the pattern that was supplied to the plugin.
• enabled Function that checks if the passed key argument is enabled by the pattern that was supplied to the plugin, returns a boolean, enabled(key).
• destroy Function that allows you to register a (async) clean-up callback which is executed when the destroy method is called.
• pattern The pattern that was supplied to the plugin as first argument.
• engine Reference to the initialized storage instance.
• options The options that was supplied to the plugin as third argument.

destroy

Destroy the initialized storage instance by removing all plugins, before, and after hooks. This will call any destroy hook that are defined by plugins but it does not trigger the clear method, so the data that you stored is untouched.

import storage from 'storage-engine';

storage.before('*', {
  setItem: () => ({
    value: 'all your values are this now, lol'
  })
});

await storage.setItem('foo', 'bar');
await storage.getItem('foo') // all your values are this now, lol

await storage.destroy();

await storage.setItem('foo', 'bar');
await storage.getItem('foo') // bar

api

Provides direct access to the AsyncStorage API that we're wrapping. This API will not execute any of the plugins or before/after modifications that are registered. This is the API we use internally to communicate with AsyncStorage.

import storage from 'storage-engine';

await storage.api('setItem', 'foo', 'bar');

The method accepts the following arguments:

• method The name of the method that needs to be executed.
• ...args The args that you would have normally passed into the original API.

---

The rest of the API methods are the API methods that exist on the AsyncStorage API that is provided by React-Native / React-Native Community. Some of the API have been enhanced to allow a more sensible argument or return format. For example, we only allow the async/await interface instead of an additional 3rd callback argument. We're just gonna go briefly over this API and make the assumption that you already have prior knowledge of the existing React-Native AsyncStorage API:

---

getItem

The getItem allows you to retrieve a previously stored value. When the value does not exist, a null will be returned instead.

const value = await storage.getItem('key');
console.log(value); // key

• key The key of the value you want to retrieve.

setItem

Stores a new item. Yup, that's it.

await storage.setItem('key', 'value');

• key The key where the value will be stored at.
• value The contents that needs to be stored, should be string, unless a plugin allows you to use a different format.

removeItem

Removes the previously stored value.

await storage.removeItem('key');

• key The key of the value you want to remove.

mergeItem

Merge the contents of the key, with the supplied value.

await storage.mergeItem('key', '{"json": "here"}');

• key The key of the value you want to update.
• value A stringified JSON object that will be merged with the existing value

clear

Removes all the data that you've stored. Everything. Gone. Forever. Like it never existed. This method is officially approved by Thanos.

await storage.clear();

getAllKeys

Retrieve all keys that are stored in the AsyncStorage.

const keys = await storage.getAllKeys();

flushGetRequests

Does anyone actually this method? Why am I even documenting this.

await storage.flushGetRequests();

multiGet

Retrieves multiple values at once.

const [one, two] = await storage.multiGet(['one', 'two']);

// one: { key: one, value: ... }
// two: { key: two, value: ... }

The data that is returned by the multi API is slightly different, as we've wrapped each item in an object which has key, and value property.

multiSet

Store multiple values at once.

await storage.multiSet([
  ['one', 'value'],
  ['two', 'another value']
]);

//
// Also supported:
//
await storage.multiSet([
  { key: 'one', value: 'value' },
  { key: 'two', value, 'another value' }
]);

The data that is returned by the multi API is slightly different, as we've wrapped each item in an object which has key, and value property.

multiMerge

Merge multiple values at once.

await storage.multiMerge([
  ['key', '{"json": "blob"}'],
  ['another', '{"cow": "moo"}']
]);

//
// Also supported:
//
await storage.multiMerge([
  { key: 'key', value: '{"json": "blob"}'},
  { key: 'another', value: '{"cow":"moo"}'}
]);

The data that is returned by the multi API is slightly different, as we've wrapped each item in an object which has key, and value property.

multiRemove

Thanos multiple keys at once.

await storage.multiRemove(['one', 'two']);

The data that is returned by the multi API is slightly different, as we've wrapped each item in an object which has key, and value property.

Debugging

The storage-engine is instrumented with the diagnostics library which will allow you to opt-in to debug logs. These can be enabled through AsyncStorage by setting the DEBUG key with a specific logger pattern that needs to be enabled.

import storage from 'storage-engine';

await storage.setItem('DEBUG', 'storage-engine*');

See diagnostics for more information.

License

MIT

Changelog

3.0.0

• Complete rewrite of internals.