This is a sub-package of web3.js.
This requestmanager package is used by most web3.js packages.
Please read the documentation for more.
npm install web3-core-requestmanager
const Web3WsProvider = require('web3-providers-ws');
const Web3RequestManager = require('web3-core-requestmanager');
const requestManager = new Web3RequestManager(new Web3WsProvider('ws://localhost:8546'));