Node.js EventEmitter and multiple levels of inheritance

Question

I'm trying to figure out the best approach to multiple levels of inheritance when using the Node.js `EventEmitter` class. The setup is I am developing an MVC framework for Node.js using Controllers that can have base Controllers, but Controllers can emit events that also emit the same event on its base Controller. So far I have: ``` var events = require('events'); var util = require('util'); var Controller = function() { }; util.inherits(Controller, events.EventEmitter); var baseController = new Controller(); baseController.on('request', function() { console.log('Calling request event on baseController'); }); var homeController = new Controller(); homeController.prototype = baseController; homeController.on('request', function() { console.log('Calling request event on homeController'); }); homeController.emit('request'); ``` ...but only "Calling request event on homeController" is output, I want both 'request' events to fire. How do I do this? Maybe I need to completely change my appr…

Accepted Answer

In your example, there is no kind of inheritance relationship between homeController and baseController. Also, this line:

```
homeController.prototype = baseController;
```

Is redundant, since the prototype property only matters for constructor functions.

If you want to set up baseController so whoever extends/ inherits from it will have the 'request' listener assigned to it, first you should define it like this:

```
var BaseController = function(){
    this.on('request', function(){
       console.log('...');
    });
};

BaseController.prototype = new events.EventEmitter();
BaseController.prototype.constructor = BaseController;
```

It will be even better if you can make the handler assignment in an initiliazation method (doing work in a constructor function is usually bad design):

```
var BaseController = function(){};

BaseController.prototype = new events.EventEmitter();
BaseController.prototype.init = function(){
    this.on('request', function(){
       console.log('...');
    });
};
```

And then, all you need to extend it in your HomeController is to do this:

```
var HomeController = function(){};
HomeController.prototype = new BaseController();

var homeController = new HomeController();
homeController.init(); // If you went with the initialization approach I offered...
```

Please note, that unless you must do it, creating long inheritance chains in JS isn't very nice or maintainable. If you can, I encourage you to avoid doing it and try finding a more maintainable solution.

Node.js EventEmitter and multiple levels of inheritance

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