Check mongoose connection state without creating new connection

I have some tests - namely Supertest - that load my Express app. This app creates a Mongoose connection. I would like to know how to check the status of that connection from within my test.

In app.js

mongoose.connect(...)

In test.js

console.log(mongoose.connection.readyState);

How to access the app.js connection? If I connect using the same parameters in test.js will that create a new connection or look for existing one?

Since the mongoose module exports a singleton object, you don't have to connect in your test.js to check the state of the connection:

// test.js
require('./app.js'); // which executes 'mongoose.connect()'

var mongoose = require('mongoose');
console.log(mongoose.connection.readyState);

ready states being:

• 0: disconnected
• 1: connected
• 2: connecting
• 3: disconnecting

I use this for my Express Server mongoDB status, where I use the express-healthcheck middleware

// Define server status
const mongoose = require('mongoose');
const serverStatus = () => {
  return { 
     state: 'up', 
     dbState: mongoose.STATES[mongoose.connection.readyState] 
  }
};
//  Plug into middleware.
api.use('/api/uptime', require('express-healthcheck')({
  healthy: serverStatus
}));

Gives this in a Postman request when the DB is connected.

{
  "state": "up",
  "dbState": "connected"
}

Gives this response when the database was shutdown.

{
"state": "up",
"dbState": "disconnected"
}

(The "up" in the responses represent my Express Server status)

Easy to read (no numbers to interpret)

As stated before "readyState" is good. "ping" is also good admin utility for doing so as well. It will return { ok: 1 } if it can accept commands.

const mongoose = require('mongoose')

// From where ever your making your connection
const connection = await mongoose.createConnection(
    CONNECT_URI,
    CONNECT_OPTS
)

async function connectionIsUp(): Promise<boolean> {
    try {
        const adminUtil = connection.db.admin()

        const result = await adminUtil.ping()

        console.log('result: ', result) // { ok: 1 }
        return !!result?.ok === 1
    } catch(err) {
        return false
    }    
} 

Or if you you want it short.

async function connectionIsUp(): Promise<boolean> {
    try {
        return await connection.db.admin().ping().then(res => !!res?.ok === 1)
    } catch (err) {
        return false
    }
}

var dbState = [{
    value: 0,
    label: "disconnected"
},
{
    value: 1,
    label: "connected"
},
{
    value: 2,
    label: "connecting"
},
{
    value: 3,
    label: "disconnecting"
}];

mongoose.connect(CONNECTIONSTRING, {
    useNewUrlParser: true
},
() => {
    const state = Number(mongoose.connection.readyState);
    console.log(dbState.find(f => f.value == state).label, "to db"); // connected to db
});