Mongodb – Mongoose Trouble Adding Subdocs to Array

I am looking to push to an array on my users schema in mongoose. I am following mongoose’s Adding Subdocs to Arrays documentation but keep getting an error on user.notes.push(newNotebook)

TypeError: Cannot read properties of undefined (reading ‘push’)

Here is my setup:

const User = require('../models/userModel')


const addNotebook = async (req, res) => {

...

const user = User.findOne({ userId })

const newNotebook = { userId: userId, notebookId: notebookId, title: title, numNotes: 0 }

user.notebooks.push(newNotebook)
        
}

Any help would be much appreciated.

Update–

Here is the solution:

const User = require('../models/userModel')


const addNotebook = async (req, res) => {

...

const user = User.findOne({ userId })

if (!user) return

const newNotebook = { userId: userId, notebookId: notebookId, title: title, numNotes: 0 }

user.notebooks = user.notebooks || []; // returns user.notebooks if defined else empty array

user.notebooks.push(newNotebook)

await user.save()
        
}

Big thanks to Mandeep for showing me the !user condition and .save() method. Special thanks to Sardar for bringing the user.notebooks = user.notebooks || [] solution to light.

Disclaimer: upon watching this video on MongoDB anti patterns, I learned nesting boundless data under a single document can be problematic since each MongoDB document is limited to 16mb. It is also supposedly inefficient relative to saving your data in respective collections. Use caution when adding subdocs to arrays.