discord.js/src/client/ClientManager.js

const Constants = require('../util/Constants');

class ClientManager {

  constructor(client) {
    this.client = client;
    this.heartbeatInterval = null;
  }

  connectToWebSocket(token, resolve, reject) {
    this.client.store.token = token;
    this.client.rest.methods.getGateway()
      .then(gateway => {
        this.client.ws.connect(gateway);
        this.client.once(Constants.Events.READY, () => resolve(token));
      })
      .catch(reject);

    setTimeout(() => reject(Constants.Errors.TOOK_TOO_LONG), 1000 * 15);
  }

  setupKeepAlive(time) {
    this.heartbeatInterval = setInterval(() => {
      this.client.ws.send({
        op: Constants.OPCodes.HEARTBEAT,
        d: Date.now(),
      });
    }, time);
  }
}

module.exports = ClientManager;