Lazy Load Singleton

Tiny library that transforms any class to singleton with lazy initialization.

Installation

npm i --save lazy-load-singleton
# or
yarn add lazy-load-singleton

Behaviour

When you wrap a class with the libary, it returns an object that has init method with signature that equals to constuctor's signature and proxies all properties accessment to class instance. This libary will be helpful in situations where your singleton is inialized base on event (e.g 'ready'), not during first code execution. You can read more details about motivation and solution in my article.

Example

Assume you have database class that accepts connection string in constructor. Your environment is event-based and you can't initialize class right away.

Singleton

import LazySingleton from 'lazy-load-singleton';

class DBConnection {
  isClosed = false;

  constructor(connectionString) {}
  performQuery(query, values) {}
}

export default LazySingleton(DBConnection)

Initialization and usage

import db from './db';

app.on('ready', config => {
  db.init(config.dbConnectionString); // #init signature equals to constructor signature
});

//...

app.on('create-user', user => {
  if (!db.isClosed) { // has access to properties
    // has access to methods
    db.performQuery(` 
      INSERT INTO users(id, name)
      VALUES($1, $2)
    `, [user.id, user.name])
  }
});