ESMapDB is an embedded database for Node.js with an ECMAScript Map interface. For lightweight operations with key-value pairs, ESMapDB combines the convenient interface of a Map with a simple, persistent data store.
Yet another database??? At reelyActive, we used NeDB, "The JavaScript Database", successfully for many years. But alas, NeDB is no longer maintained. After an extensive search for a simple, well-maintained successor with minimal dependencies, LevelDB (wrapped up in the Node.js-friendly level package) was identified as the best candidate.
So why not just LevelDB??? Well, LevelDB is very nearly functionally equivalent with the Map object introduced in ES6, so we decided to wrap LevelDB with a Map interface, which arguably results in more familiar, readable and developer-friendly code. In short, we've attempted to make managing a reasonable number of key-value pairs—with persistence—as simple as using Map.get(), Map.set() and the usual iterators.
ESMapDB can be instantiated with any combination of in-memory and/or persistent operation.
When in-memory operation is enabled, simply interact with ESMapDB like a Map, using .get(), .set(), .delete() and the iterators which function exactly like a Map.
When persistent operation is enabled, simply add a callback function as an argument to the same .get(), .set(), .delete(), ... functions, which will execute once the asynchronous filesystem operation of LevelDB completes.
When both in-memory and persistent operation are enabled, enjoy the simple non-blocking function calls of the Map interface while the filesystem operations are taken care of in the background.
npm install esmapdb
const ESMapDB = require('esmapdb');
const options = { createInMemory: true,
createPersistent: true };
let database = new ESMapDB(options);
database.set('key', 'value'); // Write to both memory and the filesystem
console.log(database.get('key')); // Prints 'value'Note that in all methods with an optional callback below, the callback function observes the form callback(err, result) where the two parameters are defined as follows:
- err: Error returned by the persistent database operation,
undefinedotherwise. - result: The same result that the function call itself returns, but taken from the persistent store, when persistent operation is enabled. If persistent operation is disabled, the result is taken from the in-memory store.
In other words, when both in-memory and persistent operation are enabled, the function call returns the result from the in-memory store while the asynchronous callback result is derived from the persistent store.
Constructor. Create a new ESMapDB instance with the given options:
| Option | Default | Description |
|---|---|---|
| createInMemory | false | Maintain an in-memory copy of the database |
| createPersistent | false | Maintain a copy of the database on the filesystem |
| persistentLocation | 'database' | Store data in a folder called 'database' |
| persistentKeyEncoding | 'utf-8' | See LevelDB for supported encodings |
| persistentValueEncoding | 'utf-8' | See LevelDB for supported encodings |
If an optional callback is provided, and the createPersistent option is selected, the callback will execute after the persistent store is loaded or an error is encountered.
As of esmapdb v0.3.0, errors encountered when loading a persistent store are no longer thrown, but may be observed in the optional callback, and operation will continue as per the createInMemory setting.
Returns the number of key/value pairs in the database. If in-memory option is enabled, the number of key/value pairs in the Map() is returned. Else, an estimate of the number of key/value pairs in persistent storage is returned.
Removes all key/value pairs from the database. Returns undefined.
If an optional callback is provided, and persistent operation is enabled, the callback will execute after the persistent store is cleared. In the absence of a persistent store, the callback will execute immediately.
Removes the pair with the given key from the database. Returns true if the pair in the database existed and has been removed, or false if the element does not exist.
If an optional callback is provided, and persistent operation is enabled, the callback will execute after deletion from the persistent store completes. In the absence of a persistent store, the callback will execute immediately.
Retrieve the value associated with the given key. Returns the value associated to the key, or undefined if there is none.
If an optional callback is provided, and persistent operation is enabled, the callback will execute after retrieval from the persistent store completes. In the absence of a persistent store, the callback will execute immediately.
Determine whether a pair with the given key exists in the database. Returns a boolean asserting whether a value has been associated to the key in the database or not.
If an optional callback is provided, and persistent operation is enabled, the callback will execute after determination from the persistent store completes. In the absence of a persistent store, the callback will execute immediately.
Create or update a key/value pair in the database. Sets the value for the key in the database and returns the updated database as a Map object. If in-memory operation is disabled, the return value will be an empty Map object.
If an optional callback is provided, and persistent operation is enabled, the callback will execute after the update of the persistent store completes. In the absence of a persistent store, the callback will execute immediately.
Returns a new Iterator object that contains the keys for each element in the in-memory database. If in-memory operation is disabled, there will be zero keys over which to iterate.
Returns a new Iterator object that contains the values for each element in the in-memory database. If in-memory operation is disabled, there will be zero values over which to iterate.
Returns a new Iterator object that contains an array of [key, value] for each element in the in-memory database. If in-memory operation is disabled, there will be zero pairs over which to iterate.
Executes the callback once for each key-value pair present in the in-memory database. If in-memory operation is disabled, there will be zero execution of the callback function.
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MIT License
Copyright (c) 2022 reelyActive
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