Rocket.Chat/app/livechat/server/methods/setUpConnection.js

import { Meteor } from 'meteor/meteor';
import { check } from 'meteor/check';

import { Livechat } from '../lib/Livechat';

Meteor.methods({
	'livechat:setUpConnection'(data) {
		check(data, {
			token: String,
		});

		const { token } = data;

		if (!this.connection.livechatToken) {
			this.connection.livechatToken = token;
			this.connection.onClose(() => {
				Livechat.notifyGuestStatusChanged(token, 'offline');
			});
		}
	},
});