CODEWITHSUNDEEP
node.jsexpressinheritance
Thibaud
Thibaud

Reputation: 35

Class member inheritance in nodejs + expressjs

I don't quite understand how class inheritance and context is working in nodejs + expressjs.

I have 3 files :

api.js 

class API {
  constructor () {
    this._id = Math.random()
    console.log("Instantiated id:" + this._id)
  }

  list (req, res, next) {
    console.log("Instantiated id:" + this._id)
  }
}
module.exports = API

user.js

const API = require('./api.js')

class UserAPI extends API {

  constructor () {
    super()
  }
}
module.exports = UserAPI

route.js

var UserAPI = require('./user.js')
var user = new UserAPI()
router.get('/', user.list);

What I would like to see is the ID when starting then the same ID each time I do a GET request. But when I do a GET request I have : ERROR: TypeError: Cannot read property '_id' of undefined

How can I have access to member in the Base class when deriving it ?

Thanks !

Upvotes: 2

Views: 1026

Answers (2)

Burawi
Burawi

Reputation: 471

Making API inheritance with express is impossible. CheckZinkyJS, it makes exactly what you want to do.

Upvotes: 0

Patrick Hund
Patrick Hund

Reputation: 20246

The problem is not class inheritance, but simply the way you use the list method. You are passing it directly to router.get, that won't work, because you are only passing a reference to the function, which then doesn't know the context of the instance of UserAPI.

You can fix this by passing an anonymous function to router.get that then executes user.list, like this:

route.js

var UserAPI = require('./user.js')
var user = new UserAPI()
router.get('/', (req, res, next) => user.list(req, res, next));

Upvotes: 2

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