Syntax for connecting to mongoose

Question

How is it possible to call multiple functions on the mongoose variable? Shouldn't moogoose be called repeatedly and invoked on appropriately?

Working Code:

//Import
const express = require("express");
const mongoose = require("mongoose");

//initialize a variable called app to express
const app = express();
// DB Config
const db = require("./config/keys").mongoURI;
// Connect to MongoDB
mongoose
  .connect(db)
  .then(() => console.log("MongoDB connected"))
  .catch(err => console.log(err));

What I thought it should be:

// Connect to MongoDB
mongoose.connect(db)
mongoose.then(() => console.log("MongoDB connected"))
mongoose.catch(err => console.log(err));

Answer 1

Connecting to mongoose returns a promise (the connect() function). You need to wait for this to resolve before you can proceed. That's the reason why you chain .then on the connect() function and not on the mongoose variable since the mongoose variable itself is not a promise. The bottom piece of code doesn't wait for the connection to occur at all and doesn't call .then on a promise.

If you are confused on what the .then and .catch functions do exactly read more about promises here: Promise and Promise chaining (MDN)