(node:31873) UnhandledPromiseRejectionWarning: TypeError: Item is not a constructor

Whenever I want to make a POST request using Postman I get this error: TypeError: Item is not a constructor. Any idea why? I have my code here:

const Item = require('../model/item.js');

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

    const category = await categoryService.findCategoryByName(req.body.category);
    const newItem = new Item({
        name: req.body.name,
        created: new Date(),
        category: [category],
        quantity: req.body.quantity,
    });

    try{
        await newItem.save();

        res.status(201).json(newItem);
    }catch(error){
        res.status(404).json({message: error.message});
    }
};

And item.js:

const mongoose = require('mongoose');
const categSchema = require("./category.js")

const itemSchema = mongoose.Schema({
    name: {type: String, required: true},
    created: {type: Date, required: true, unique: true},
    category: [categSchema.categorySchema],
    quantity: {type: Number, required: true}
});

var itemData = mongoose.model("itemData", itemSchema);
module.exports.itemData = itemData;
module.exports.itemSchema = itemSchema;

Answer

You’re importing the full exports object, not just part of it. That object is not a constructor function (it’s not a function at all).

Looking at your exports: According to the documentation (I don’t use Mongoose), mongoose.model returns a constructor function. So:

1. Export it using standard naming for constructor functions (ItemData, rather than itemData), and

2. Import it rather than the entire exports object

So for instance:

module.exports.ItemData = mongoose.model("itemData", itemSchema);
module.exports.itemSchema = itemSchema;

and to import it (by destructuring it from the exports object):

const { ItemData } = require("../model/item.js");
//    ^−−−−−−−−−−^−−−−−−−−− destructuring

Then, new ItemData should work.

Alternatively, import the whole thing (const item = require(/*...*/);) and then use new item.ItemData.