NodeJS Construct a custom object without requiring the file - node.js

Question

Is there a way in nodejs to define a custom object type in it's own file, then instantiate it anywhere else in the codebase without needing to require in the file?
For example, every time I create a new map somewhere, I don't have to require in the map definition. I want to be able to do
var user = new User();
from anywhere without requiring in the definition.

Answer 1

If you don't want to require a dependency everywhere then you could use Dependency Injection. Dependency Injection is a pattern for passing dependencies or common information from one context to another.
The power of Dependency Injection is decoupling the Dependency itself with resolving and/or initializing that Dependency. In JavaScript, closures can be used to hide configuration/initialization details of a Dependency by locking in their context to the scope that created them. This means that your files implementing the Dependency don't need to be concerned with how to get it initialized (ie. a config) which, probably also means more thing it needs to require.
Below is an example of how a User can be required in one file, injected into a separate file and then be used as if it were required within the file it was injected to. I chose to use an Express Server and Dependency Injection into a Router as the example because a popular reason to use Node.js is to build a Web API. For another example of Dependency Injection, see this blog post from RisingStack Engineering (you'll need to scroll down to the Dependency Injection section).
The example has 3 files
lib/models/User.js
This is the module that is Injected into our UserRouter
/routes/user.js
This is the UserRouter and it returns a function that accepts a models object which, contains all Models the UserRouter needs. Once the router is created it is returned for use within an Express Server
server.js.
The Express Server that is going to be responsible for injecting the User Model into the UserRouter so it can create new users in a cache.
lib/models/User
class User {
constructor(name) {
this.name = name
}
}
module.exports = User
routes/user.js
const Router = require('express').Router
const UserRouter = models => {
// Use Destructuring to get the User model from the models object passed into the Router
// You can use regular ES5 for this as well: var User = models.User
const {User} = models
const router = new Router()
const users = []
// Return all users in cache
router.get('/', (req, res) => res.status(200).json({users}))
router.post('/', (req, res) => {
const {name} = (req.body || {})
if (!name) {
return res.status(400).send('A User must have a name')
}
// Create the new User
let newUser = new User(name)
// add it to the users cache
users.push(newUser)
// return 201 CREATED and send the user as the message body
return res.status(201).json(newUser)
})
// Return the router instance
return router
}
module.exports = UserRouter
server.js
const express = require('express')
const port = process.env.PORT || 1337
// require our UserRouter
const UserRouter = require('./routes/user')
// import the User model
const User = require('./lib/models/User')
// create an object called Models with the User now as a property
const Models = {User}
const server = express()
// Inject the Models directly into the UserRouter
server.use('/users', UserRouter(Models))
server.listen(port, () => console.log(`Listening on ${port}`))