How to implement inheritance in node.js modules? - node.js

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
}
});
};