How to implement inheritance in node.js modules?

Question

I am in process of writing nodejs app. It is based on expressjs. I am confused on doing inheritance in nodejs modules. What i am trying to do is create a model base class, let's say my_model.js.

module.exports = function my_model(){
  my_model.fromID = function(){
    //do query here
  }
}

Now i want to use those methods in my_model in my other model class. let's say user_model.js How do i inherit my_model in user_model?

Answer 1

in base_model:

function BaseModel() { /* ... */ }

BaseModel.prototype.fromID = function () { /* ... */ };

module.exports = BaseModel;

in user_model:

var BaseModel = require('relative/or/absolute/path/to/base_model');

function UserModel() {
    UserModel.super_.apply(this, arguments);
}

UserModel.super_ = BaseModel;

UserModel.prototype = Object.create(BaseModel.prototype, {
    constructor: {
        value: UserModel,
        enumerable: false
    }
});

UserModel.prototype.yourFunction = function () { /* ... */ };

module.exports = UserModel;

---

Instead of using Object.create() directly, you can also use util.inherits, so your user_model becomes:

var BaseModel = require('relative/or/absolute/path/to/base_model'),
    util = require('util');

function UserModel() {
    BaseModel.apply(this, arguments);
}

util.inherits(UserModel, BaseModel);

UserModel.prototype.yourFunction = function () { /* ... */ };

module.exports = UserModel;

Answer 2

With ES6 the usage of util.inherits() is discouraged in favor of ES6 class and extends

const EventEmitter = require('events');

class MyStream extends EventEmitter {
  constructor() {
    super();
  }
  write(data) {
    this.emit('data', data);
  }
}

const stream = new MyStream();

stream.on('data', (data) => {
  console.log(`Received data: "${data}"`);
});
stream.write('With ES6');

Answer 3

Using utility.inherits can also help you decouple the child from the parent.

Instead of calling the parent explicitly, you can use super_ to call the parent.

var BaseModel = require('relative/or/absolute/path/to/base_model'),
util = require('util');

function UserModel() {
   this.super_.apply(this, arguments);
}

util.inherits(UserModel, BaseModel);

utility.inherits source:

var inherits = function (ctor, superCtor) {
ctor.super_ = superCtor;
ctor.prototype = Object.create(superCtor.prototype, {
    constructor: {
        value: ctor,
        enumerable: false
        }
    });
};