db.js

const pg = require('pg');
pg.defaults.ssl = process.env.DATABASE_URL ? process.env.DATABASE_UR: true;
// create a config to configure both pooling behavior
// and client options
// note: all config is optional and the environment variables
// will be read if the config is not present
var urlMatch = /postgres:\/\/(\w+):(\w+)@(.+):(.+)\/(.+)/;
var match = urlMatch.exec(process.env.DATABASE_URL);
var config = {
    user: match[1], //env var: PGUSER
    database: match[5], //env var: PGDATABASE
    password: match[2], //env var: PGPASSWORD
    host: match[3], // Server hosting the postgres database
    port: match[4], //env var: PGPORT
    max: 10, // max number of clients in the pool
    //idleTimeoutMillis: 30000, // how long a client is allowed to remain idle before being closed
};
//this initializes a connection pool
//it will keep idle connections open for 30 seconds
//and set a limit of maximum 10 idle clients
const pool = new pg.Pool(config);

pool.on('error', function (err, client) {
    // if an error is encountered by a client while it sits idle in the pool
    // the pool itself will emit an error event with both the error and
    // the client which emitted the original error
    // this is a rare occurrence but can happen if there is a network partition
    // between your application and the database, the database restarts, etc.
    // and so you might want to handle it and at least log it out
    console.error('idle client error', err.message, err.stack);
});

//export the query method for passing queries to the pool
module.exports.query = function (text, values, callback) {
    return pool.query(text, values, callback);
};

// the pool also supports checking out a client for
// multiple operations, such as a transaction
module.exports.connect = function (callback) {
    return pool.connect(callback);
};