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I am working on a home automation project in NodeJS with several modules. These modules need access to data devices within a central DeviceManager. Normally I would create a singleton for this purpose so all modules access the same state of the DeviceManager.

To create a singleton I use:

class DevicesManagerInstance {

    constructor() {

        this.devices = {};

    }

    addDevice(id, device) {
        this.devices.id = device;
    }

}

let DevicesManagerInstance = new DevicesManager();

module.exports = DevicesManagerInstance;

I've found some older questions regarding singletons and sharing data but still not satisfied with the answer to the question if it is de NodeJS way to share data:

But also read singletons are an anti-pattern. Can someone clarify what is the "NodeJS" way of sharing data between modules (in my case the devices). In Angular I would create a service for this purpose.

Bas van Dijk
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2 Answers2

4

Why fix what isn't broken? If your approach works, it works.

That being said, I don't see any reason to create a class if I'm only going to create one instance. I would opt for a different approach:

var DeviceManager = {
    devices: {},
    addDevice(id, device) { // this is valid syntax
        DeviceManager.devices[id] = device;
    }
};
module.exports = DeviceManager;

or, if you don't want devices to be available outside of the module:

var devices = {};
var DeviceManager = {
    addDevice(id, device) { // this is valid syntax
        devices[id] = device;
    }
};
module.exports = DeviceManager;
EKW
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  • What about the constructor part. My example is simplified in the real class there a lot of operations and initialisation going on. Do you just create for example a init function? – Bas van Dijk Aug 31 '17 at 06:59
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    Why create an init function when the only time you'll be initializing something is when you're defining it? Personally, I would initialize everything when I defined DeviceManager. – EKW Aug 31 '17 at 11:26
2

This is a single instance but if you need class you can also convert the following to class structure easily,

var DeviceManager = function() {
      this.devices: [];  // constructor
};

DeviceManager.prototype.addDevice = function(id, device) {
             DeviceManager.devices[id] = device;          
};
var deviceManager = new DeviceManager();
module.exports = deviceManager;

You can access the devices in other modules as 

var DeviceManager = require('./devicemanager');
DeviceManager.devices; // accessing devices
Bharathvaj Ganesan
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  • What about the constructor part. My example is simplified in the real class there a lot of operations and initialisation going on. Do you just create for example a init function? – Bas van Dijk Aug 31 '17 at 06:59
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    I have updated the script @BasvanDijk You now have access to that instance and there is only one **DeviceManager** instance. – Bharathvaj Ganesan Aug 31 '17 at 07:05