Cannot access 'pool' before initialization

Question

I am currently experimenting with passing queries from postgres database and loading it into a page. I have setup a test page with the following code below :

const sql_query = require('../sql');
var express = require('express');
var router = express.Router();

const { Pool } = require('pg')
const pool = new pool ({
    connectionString: process.env.DATABASE_URL
});


pool.query('SELECT * FROM rides', [1], (err, res) => {
  if (err) {
    throw err
  }
  console.log('user:', res.rows[0])
})



module.exports = router;

However, when i run npm test, the stack trace is as follows:

/Users/lawjiahua/Desktop/CS2102_proj/App/routes/testPage.js:6
const pool = new pool ({
             ^

ReferenceError: Cannot access 'pool' before initialization
    at Object.<anonymous> (/Users/lawjiahua/Desktop/CS2102_proj/App/routes/testPage.js:6:14)
    at Module._compile (internal/modules/cjs/loader.js:945:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:962:10)
    at Module.load (internal/modules/cjs/loader.js:798:32)
    at Function.Module._load (internal/modules/cjs/loader.js:711:12)
    at Module.require (internal/modules/cjs/loader.js:838:19)
    at require (internal/modules/cjs/helpers.js:74:18)
    at Object.<anonymous> (/Users/lawjiahua/Desktop/CS2102_proj/App/app.js:25:22)
    at Module._compile (internal/modules/cjs/loader.js:945:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:962:10)

Here is my part of my main app file

var createError = require('http-errors');
var express = require('express');
var path = require('path');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var logger = require('morgan');
const pg = require('pg');

var app = express();

require('dotenv').config();

/* PAGES FOR THE PROJECT */
var indexRouter = require('./routes/index');
var usersRouter = require('./routes/users');
var driverRouter = require('./routes/driver');
var awaitingApprovalRouter = require('./routes/awaitingApproval');
var registerDriverRouter = require('./routes/registerDriver');
var ridesRouter = require('./routes/rides');
var homepageRouter = require('./routes/homepage');


app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
var testPageRouter = require('./routes/testPage');


// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'ejs');

app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

/* FOR PROJECT */
app.use('/', indexRouter);
app.use('/driver', driverRouter);
app.use('/awaitingApproval', awaitingApprovalRouter);
app.use('/registerDriver', registerDriverRouter);
app.use('/rides', ridesRouter);
app.use('/homepage', homepageRouter);


app.use('/testpage', testPageRouter);

module.exports = app;

What does the error refer to? Do i have to initialise pool in the app.js page in order to use it in routes?

Ed Bangga · Accepted Answer · 2019-10-21 05:19:31Z

1

if you are creating an object with your module Pool, it should be upper case.

const { Pool } = require('pg')
const pool = new Pool ({
    connectionString: process.env.DATABASE_URL
});


pool.query('SELECT * FROM rides', [1], (err, res) => {
  if (err) {
    throw err
  }
  console.log('user:', res.rows[0])
})

answered Oct 21, 2019 at 5:19

Ed Bangga

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