An IDBMap also extends EventTarget too, so dispatchEvent is also available, among others. Handled events are by default abort, close, error and versionchange.

The IDBMap constructor is the only main different API compared to Map:

it accepts a database's name suffix as string. The DB will be called 'IDBMap/${name}'. The storage name used for this db will be entries. An empty string is also a valid name but please be aware of naming collisions
it accepts an optional options object, currently to either override transactions' durability, where its default value is 'default', or to use a different database prefix name which default value is 'IDBMap'

type IDBMapOptions = {
    durability?: 'strict' | 'relaxed' | 'default';
    prefix?: string;
}

class IDBMap extends EventTarget implements Map {
  constructor(
    name:string,
    options:IDBMapOptions = { durability: 'default', prefix: 'IDBMap' }
  ):IDBMap

  // the only extra method not present in Map or EventTarget
  close():Promise<void>
}

Example

import IDBMap from '@webreflection/idb-map';

// create an async map with a generic storage name
const idbMap = new IDBMap('my-storage-name');

// check any Map property by awaiting it
console.log(await idbMap.size);
console.log(await idbMap.has('nope'));

// optional helpers for buffered data
const encoder = new TextEncoder;
const decoder = new TextDecoder;

// set any IDB compatible value
await idbMap.set('test.txt', 'test value');
console.log(await idbMap.has('test.txt'));
await idbMap.set('other.txt', encoder.encode('other value'));

// get any IDB stored value
console.log(await idbMap.get('test.txt'));
console.log(decoder.decode(await idbMap.get('other.txt')));

// retrieve any other async Map API method
console.log(await idbMap.keys());
console.log(await idbMap.size);
for (const entry of await idbMap.entries())
    console.log(entry);

// or remove a single key
await idbMap.delete('other.txt');
console.log(await idbMap.keys());
console.log(await idbMap.size);

// or clear the whole thing
await idbMap.clear();
console.log(await idbMap.keys());
console.log(await idbMap.size);

// eventually close it
await idbMap.close();

Background / Goal / Why

There are other projects with a similar goal, most popular or notable is idb-keyval, but ...

there is no familiar API around this topic, everyone offering "easy IndexedDB" is kinda proposing a new API
there is nothing more similar than a JS' Map to actually store key / value pairs
the Map API is nothing new to learn, here the IDBMap is just about the same except it's inevitably asynchronous ... but ...
- it is still possible via coincident to have this transparently synchronous from a worker (if that's your cup of tea), making the Map a 1:1 familiar primitive that will persist its data in user's space
the IDBMap also extends EventTarget, forwarding internal events when/if needed
the IDBMap adds a .close() asynchronous method to ensure a db has been successfully closed