This is a trivial, isomorphic, straightforward, TypeScript-compatible singleton implementation:

• NO dependencies
• lazily created on first use, as expected

Typical usage is when one wants to share a common object, for ex. a connection to a database, yet is able to create it if not already existing.

This lib is NOT a memoization lib in the sense that in this lib, subsequent calls with different parameters (if any) will still yield the first invocation result.

Be sure to review your options before using the singleton pattern! While there are legitimate uses, it can also be a code smell close to a global variable!

See also:

• memoize-one if you simply want a single call

Usage

// "@offirmo/tiny-singleton": "^1",

import tiny_singleton from '@offirmo/tiny-singleton'

// underlying function: exemple of a DB client is a correct case where the singleton pattern can be useful
function create_db_client(ip: string, logger: Console = console): DBClient {
	return ...
}

// example 1: best semantic
const get_db_client = tiny_singleton(() => create_db_client('127.0.0.1'))
get_db_client().read(1234).then(...)

// example 2: with params (not recommended as the params will only affect the 1st call, but sometimes convenient)
const get_db_client = tiny_singleton(create_db_client)

// alternative (not better, just an alternative example)
const get_db_client = tiny_singleton((options?: CreationOptions) => create_db_client(options.ip || '127.0.0.1'))

// usage
get_db_client('127.0.0.1')
get_db_client('1.2.3.4') // XXX This will return the same as above!! No new instance creation.
get_db_client().write('hello').then(...)