How to use the sharedb.DB function in sharedb

'use strict';

/* eslint id-length: ["off"], newline-per-chained-call: ["off"] */

const Pg = require('pg');
const URL = require('url');
const ShareDBDB = require('sharedb').DB;

Pg.on('end', onPgEnd);

const pgPool = new Pg.Pool(parseDatabaseURL());

class ShareDBPGCanvas extends ShareDBDB {
  commit(orgID, canvasID, op, snapshot, options, cb) {
    return pgPool.connect().then(client => {
      return client.query('BEGIN').then(_ => {
        return this.doGetSnapshot(client, orgID, canvasID, [], options)
          .then(existingSnap => {
            if (snapshot.v !== existingSnap.v + 1) return false;
            return this.doCommit(client, canvasID, op, snapshot);
          }).then(success => {
            return client.query('COMMIT').then(_ => {
              return resolveQuery(success, cb, client);

var async = require('async');
var mongodb = require('mongodb');
var DB = require('sharedb').DB;

module.exports = ShareDbMongo;

function ShareDbMongo(mongo, options) {
  // use without new
  if (!(this instanceof ShareDbMongo)) {
    return new ShareDbMongo(mongo, options);
  }

  if (typeof mongo === 'object') {
    options = mongo;
    mongo = options.mongo;
  }
  if (!options) options = {};

  // pollDelay is a dodgy hack to work around race conditions replicating the

/* 	MySQL-backed ShareDB (https://github.com/share/sharedb) database
*	Wraps https://www.npmjs.com/package/mysql
*	@author Win Min Tun (sawrochelais@gmail.com)
*	@version 1.0.5
*/

// @TODO: add support for MySQL JSON type
var DB = require('sharedb').DB;
var mysql = require('mysql');

var pool;
var mysql_config;

var ops_table;
var snapshots_table;
var debug = false;
	
// options = { db: { host: 'localhost', user: 'root', password: '', database: 'somedb', connectionLimit: 10 }, ops_table: 'ops_table_name', snapshots_table: 'snapshots_table_name', debug: false }
// connectionLimit [default=10], debug [default=false], ops_table[default=ops], snapshots[default=snapshots] are optional
function MySQLDB(options) {
	if (!(this instanceof MySQLDB)) return new MySQLDB(options);
	DB.call(this, options);

	this.closed = false;

var DB = require('sharedb').DB;
var pg = require('pg');

// Postgres-backed ShareDB database

function PostgresDB(options) {
  if (!(this instanceof PostgresDB)) return new PostgresDB(options);
  DB.call(this, options);

  this.closed = false;

  this.pg_config = options;
};
module.exports = PostgresDB;

PostgresDB.prototype = Object.create(DB.prototype);

var async = require('async');
var mongodb = require('mongodb');
var DB = require('sharedb').DB;
var OpLinkValidator = require('./op-link-validator');

module.exports = ShareDbMongo;

function ShareDbMongo(mongo, options) {
  // use without new
  if (!(this instanceof ShareDbMongo)) {
    return new ShareDbMongo(mongo, options);
  }

  if (typeof mongo === 'object') {
    options = mongo;
    mongo = options.mongo;
  }
  if (!options) options = {};