flat-cache

> A simple key/value storage using files to persist the data


Features

- A simple key/value storage using files to persist the data
- Uses a in-memory cache (via CacheableMemory) as the primary storage and then persists the data to disk
- Automatically saves the data to disk via persistInterval setting. Off By Default
- Uses expirationInterval to check for expired items in the cache. If it is not set it will do a lazy check on get or getKey
- Easily Loads the data from disk and into memory with load or loadFile
- Uses ttl and lruSize to manage the cache and persist the data
- Only saves the data to disk if the data has changed even when using persistInterval or calling save()
- Uses flatted to parse and stringify the data by default but can be overridden using serialize and deserialize in options
- ESM and CommonJS support with TypeScript typings and maintained regularly!

Table of Contents

- Installation
- Getting Started
- Breaking Changes from v5 to v6
- Global Functions
- FlatCache Options (FlatCacheOptions)
- API
- Events (FlatCacheEvents)
- Parse and Stringify for File Caching
- Loading Data via Streams
- How to Contribute
- License and Copyright

Installation

``bash
npm install flat-cache
`

Getting Started

`javascript
import { FlatCache } from 'flat-cache';
const cache = new FlatCache();
cache.setKey('key', 'value');
cache.save(); // Saves the data to disk
`

lets add it with ttl, lruSize, and persistInterval
`javascript
import { FlatCache } from 'flat-cache';
const cache = new FlatCache({
ttl: 60 60 1000 , // 1 hour
lruSize: 10000, // 10,000 items
expirationInterval: 5 1000 60, // 5 minutes
persistInterval: 5 1000 60, // 5 minutes
});
cache.setKey('key', 'value');
`

This will save the data to disk every 5 minutes and will remove any data that has not been accessed in 1 hour or if the cache has more than 10,000 items. The expirationInterval will check every 5 minutes for expired items and evict them. This is replacement to the save() method with a prune option as it is no longer needed due to the fact that the in-memory cache handles pruning by ttl expiration or lruSize which will keep the most recent there.

here is an example doing load from already existing persisted cache using the createFromFile function:

`javascript
import { createFromFile } from 'flat-cache';
const cache = createFromFile('./cacheAltDirectory/cache1');
`

You can also use the legacy load function to do this:

`javascript
import { FlatCache } from 'flat-cache';
const cache = new FlatCache();
cache.load('cache1', './cacheAltDirectory');
`
or

`javascript
import { FlatCache } from 'flat-cache';
const cache = new FlatCache({ cacheDir: './cacheAltDirectory' });
cache.load('cache1');
`

This will load the cache from the ./cacheAltDirectory directory with the cache1 id. If it doesnt exist it will not throw an error but will just return an empty cache.

Breaking Changes from v5 to v6

There have been many features added and changes made to the FlatCache class. Here are the main changes:
- FlatCache is now a class and not a function which you can create instances of or using legacy method load, loadFile, or create
- FlatCache now uses CacheableMemory as the primary storage and then persists the data to disk
- FlatCache now uses ttl and lruSize to manage the cache and persist the data
- FlatCache now uses expirationInterval to check for expired items in the cache. If it is not set it will do a lazy check on get or getKey
- getKey still exists but is now is an alias to get and will be removed in the future
- setKey still exists but is now is an alias to set and will be removed in the future
- removeKey still exists but is now is an alias to delete and will be removed in the future

Here is an example of the legacy method load:
`javascript
const flatCache = require('flat-cache');
// loads the cache, if one does not exists for the given
// Id a new one will be prepared to be created
const cache = flatCache.load('cacheId');
`

Now you can use the load method and ES6 imports:
`javascript
import { FlatCache } from 'flat-cache';
const cache = new FlatCache();
cache.load('cacheId');
`
If you do not specify a cacheId it will default to what was set in FlatCacheOptions or the default property cacheId of cache1 and default cacheDir of ./cache.

If you want to create a new cache and load from disk if it exists you can use the create method:
`javascript
import { create } from 'flat-cache';
const cache = create({ cacheId: 'myCacheId', cacheDir: './mycache', ttl: 60 60 1000 });
`

Global Functions

In version 6 we attempted to keep as much as the functionality as possible which includes these functions:

- create(options?: FlatCacheOptions) - Creates a new cache and will load the data from disk if it exists
- createFromFile(filePath, options?: FlatCacheOptions) - Creates a new cache from a file
- clearCacheById(cacheId: string, cacheDir?: string) - Clears the cache by the cacheId on the file system not in memory.
- clearAll(cacheDirectory?: string) - Clears all the caches




FlatCache Options (FlatCacheOptions)


- ttl? - The time to live for the cache in milliseconds. Default is 0 which means no expiration
- lruSize? - The number of items to keep in the cache. Default is 0 which means no limit
- useClone? - If true it will clone the data before returning it. Default is false
- expirationInterval? - The interval to check for expired items in the cache. Default is 0 which means no expiration
- persistInterval? - The interval to save the data to disk. Default is 0 which means no persistence
- cacheDir? - The directory to save the cache files. Default is ./cache
- cacheId? - The id of the cache. Default is cache1
- serialize? - The function to parse the data. Default is flatted.parse
- deserialize? - The function to stringify the data. Default is flatted.stringify

API

- cache - The in-memory cache as a CacheableMemory instance
- cacheDir - The directory to save the cache files
- cacheId - The id of the cache
- cacheFilePath - The full path to the cache file
- cacheDirPath - The full path to the cache directory
- persistInterval - The interval to save the data to disk
- changesSinceLastSave - If there have been changes since the last save
- load(cacheId: string, cacheDir?: string) - Loads the data from disk
- loadFile(pathToFile: string) - Loads the data from disk
- loadFileStream(pathToFile: string, onProgress: function, onEnd: function, onError?: function) - Loads the data from disk as a stream
- all() - Gets all the data in the cache
- items() - Gets all the items in the cache
- keys() - Gets all the keys in the cache
- setKey(key: string, value: any, ttl?: string | number) - (legacy) Sets the key/value pair in the cache
- set(key: string, value: any, ttl?: string | number) - Sets the key/value pair in the cache
- getKey(key: string) - Gets the value for the key or the default value
- get(key: string) - Gets the value for the key or the default value
- removeKey(key: string) - Removes the key from the cache
- delete(key: string) - Removes the key from the cache
- clear() - Clears the cache
- save(force? boolean) - Saves the data to disk. If force is true it will save even if changesSinceLastSave is false
- destroy() - Destroys the cache and remove files

Events (FlatCacheEvents)

Events have been added since v6 to allow for more control and visibility into the cache. Here are the events that are available:

- on(event: 'save', listener: () => void) - Emitted when the cache is saved
- on(event: 'load', listener: () => void) - Emitted when the cache is loaded
- on(event: 'delete', listener: (key: string) => void) - Emitted when the cache is changed
- on(event: 'clear', listener: () => void) - Emitted when the cache is cleared
- on(event: 'destroy', listener: () => void) - Emitted when the cache is destroyed
- on(event: 'error', listener: (error: Error) => void) - Emitted when there is an error

Here is an example of how to use the error events:

`javascript
import { FlatCache, FlatCacheEvents } from 'flat-cache';
const cache = new FlatCache();
cache.on(FlatCacheEvents.error, (error) => {
console.error(error);
});
`

FlatCacheEvents is an enum that contains the event names for the on method. You do not have to use it but makes it easier to know what events are available.

Parse and Stringify for File Caching

By default flat-cache uses flatted to parse and stringify the data. This is to allow for more complex data structures to be saved to disk. If you want to override this you can pass in your own parse and stringify functions. Here is an example:

`javascript
import { FlatCache } from 'flat-cache';
const cache = new FlatCache({
deserialize: JSON.parse,
serialize: JSON.stringify,
});
`

This will use JSON.parse and JSON.stringify to parse and stringify the data. This is useful if you want to use a different library or have a custom way of parsing and stringifying the data.

NOTE: This could cause issues if you are trying to load data that was saved with a different parser or stringifier.

Loading Data via Streams

Because of some large files we have added a helper function to load data from a file using streams. This is useful if you have a large file and want to load it in chunks. Here is an example:

`javascript
import { FlatCache } from 'flat-cache';
const cache = new FlatCache();
let progressCount = 0;
const onProgress = (progress: number, total: number) => {
progressCount++;
};

let errorCount = 0;
const onError = (error: Error) => {
errorCount++;
};

let endCount = 0;
const onEnd = () => {
console.log(Loaded ${progressCount} chunks with ${errorCount} errors.);
};
cache.loadFileStream('/path/to/cache/file', onProgress, onEnd, onError);
`
This will load the data from the file in chunks and emit the onProgress, onEnd, and onError events. You can use these events to track the progress of the loading and handle any errors that may occur.

How to Contribute

You can contribute by forking the repo and submitting a pull request. Please make sure to add tests and update the documentation. To learn more about how to contribute go to our main README https://github.com/jaredwray/cacheable. This will talk about how to Open a Pull Request, Ask a Question, or Post an Issue`.

License and Copyright

MIT © Jared Wray