The author of this article uses singletons for the service layer in this example Node api:
https://html5hive.org/how-to-create-rest-api-with-node-js-and-express/
He states, "We only want there to ever be one instance of our player service, so instead of exporting the class itself, we’ll export a new instance of it. Module files in node are only ever executed once, so this effectively gives us a singleton."
'use strict';
var uuid = require('node-uuid');
class PlayersService {
constructor() {
this.players = [];
}
getPlayers() {
return this.players;
}
getSinglePlayer(playerId) {
var player = this.players.filter(p => p.id === playerId)[0];
return player || null;
}
addPlayer(info) {
// prevent a bit of bad/duplicate data
if (!info || this.players.filter(p => (p.firstName === info.firstName && p.lastName === info.lastName)).length > 0) {
return false;
}
info.id = uuid.v4();
this.players.push(info);
return true;
}
updatePlayer(playerId, info) {
var player = this.getSinglePlayer(playerId);
if (player) {
player.firstName = info.firstName ? info.firstName : player.firstName;
player.lastName = info.lastName ? info.lastName : player.lastName;
player.displayName = info.displayName ? info.displayName : player.displayName;
return true;
}
return false;
}
}
module.exports = new PlayersService();
Which seems reasonable since the function of these services is to provide the same implementation for the controllers that use them.
However, in this post:
On Design Patterns: When to use the Singleton?
the poster asks for a legitimate use case for singletons other than a Logger class. Several people responded to his question by saying that singletons should never be used.
But isn't the use of singletons for services like the one I've copied here a legitimate use case and a best practice so that you are not creating multiple instances that provide the same implementation? Thanks.
