untested code fragments for Postgres NOTIFY and LISTEN from nodejs

gistfile1.txt

# untested code fragments for Postgres NOTIFY and LISTEN from nodejs

const {Pool, Client} = require('pg')
const dbUsername = 'dbusername'
const dbHost = '127.0.0.1'
const dbPort = '5432'
const dbPassword = 'supersecret'
const dbDatabasename = 'dbname'
const connectionString = `postgresql://${dbUsername}:${dbPassword}@${dbHost}:${dbPort}/${dbDatabasename}`
const pool = new Pool({connectionString})
const util = require('util')
import get from 'lodash.get'

pool.on('acquire', () => console.log("database: client is checked out from the pool"))
pool.on('connect', () => console.log("database: pool established new client connection to back end"))
pool.on('remove', () => console.log("database: client is closed & removed from the pool "))
pool.on('error', () => console.log("database: pool error"))

const config = {
    application_name: "nodejs",
    connectionString: connectionString, // e.g. postgres://user:password@host:5432/database
    max: 20,
}


class postgresNotificationListener {

    // we deliberately drop the connection when the listening ends, and reestablish when it starts again

    // we cannot use the pool, must use a client for notifications because we need to hold the connection open

    client: any;

    connect = () => {
        return new Promise(async (resolve: any, reject: any) => {
            this.client = new Client(config);
            await this.client.connect()
            resolve()
        })
    }

    stopListening = () => {
        return new Promise(async (resolve: any, reject: any) => {
            console.log('database: stopListening')
            await this.client.removeAllListeners();
            await this.client.end();
            this.client = undefined;
            resolve()
        })
    };

    startListening = (channel: any, callback?: Function) => {
        return new Promise(async (resolve: any, reject: any) => {
            console.log('database: startListening')
            if (!this.client) {
                await this.connect();
            }
            this.client.query(`LISTEN ${channel}`)
            this.client.on('notification', (notification: any) => {
                console.log(notification.channel)
                console.log("database: HEARD A MESSAGE: ", notification.payload)
                if (!!callback) callback(decodeURIComponent(notification.payload));
                resolve(decodeURIComponent(notification.payload));
            })
        })
    };

}


const sendPostgresNotify = (channel: any, payload: any) => {
    return new Promise(async (resolve: any, reject: any) => {
        try {
            console.log(`NOTIFY ${channel}, ${payload}`)
            if (typeof payload !== "string") throw("notification payload must be a string")
            await pool.query(`NOTIFY ${channel}, '${encodeURIComponent(payload)}'`)
            resolve();
        } catch (e) {
            console.log(e.stack)
        }
    })
};