How to implement inheritance in Screeps objects?

Question

I had been playing with Screeps for some time, and last night I decided to develop some of my behaviors in the class hierarchy, getting two classes - Miner and Transporter from the main Creep class. However when i do

console.log(_.functions(minerInstance)); 

I get the same list of functions as when working

 console.log(_.functions(transporterInstance)); 

Can someone tell me that I am doing something wrong OR, if I really encounter a limitation of the environment in which my code works? This is my code:

 //////////////////////////// // Creep.js var Creep = function(creep, room) { this.creep = creep; this.room = room; this.name = creep.name; this.id = creep.id; }; module.exports = Creep; Creep.prototype = { tick: function() { console.log("Base class implementation of tick(), should never happen."); }, getRole: function() { return this.creep.memory.role; } }; //////////////////////////// // Miner.js var Creep = require("Creep"); var Miner = function(creep, room) { this.base = Creep; this.base(creep, room); //Creep.call(this, creep, room); }; module.exports = Miner; Miner.prototype = Creep.prototype; Miner.prototype.tick = function() { var creep = this.creep; if (creep.memory.activity === undefined || creep.memory.activity === "") { var target = creep.pos.findNearest(Game.SOURCES_ACTIVE); this.mine(creep, target); } var act = creep.memory.activity; if (act == "mine") { var target = this.getTarget(creep); if (target !== undefined) { if (creep.energy < creep.energyCapacity) { creep.moveTo(target); creep.harvest(target); } else { console.log("Write dump to truck code"); /*var trucks = find.transporterInRange(creep, 1); if (trucks.length) { creep.moveTo(trucks[0]); var amount = trucks[0].energyCapacity - trucks[0].energy; creep.transferEnergy(trucks[0], amount); }*/ } } } }; Miner.prototype.mine = function(creep, target) { creep.memory.target = target.id; creep.memory.activity = "mine"; }; Miner.prototype.getTarget = function(creep) { return Game.getObjectById(creep.memory.target); }; //////////////////////////// // Transporter.js var Creep = require("Creep"); var Transporter = function(creep, room) { Creep.call(this, creep, room); }; module.exports = Transporter; Transporter.prototype = Creep.prototype; Transporter.prototype.tick = function() { var creep = this.creep; if (creep.energy < creep.energyCapacity) { var miner = this.room.findByRole(creep, "miner"); console.log(miner); if (miner !== null) { //console.log(miner[0].name); //creep.moveTo(miner); } else console.log("no miners found"); } else { console.log("moving to drop"); //var drop = find.nearestEnergyDropOff(creep); //creep.moveTo(drop); //creep.transferEnergy(drop); } }; 

Answer 1

Using this line ...

 Miner.prototype = Creep.prototype; 

... you tell JS that both prototypes are actually the same object. Therefore, any update for Miner.prototype will also affect Creep.prototype .

One possible approach is to use Object.create to establish communication between prototypes. Here is a simplified example:

 function Foo(a) { this.a = a; } Foo.prototype.tick = function() { console.log('Foo ticks'); }; Foo.prototype.tock = function() { console.log('Foo tocks'); }; function Bar(a, b) { this.base = Foo; this.base(a); this.b = b; } Bar.prototype = Object.create(Foo.prototype); // as you inherit all the properties, you'll have to reassign a constructor Bar.prototype.constructor = Bar; Bar.prototype.tick = function() { console.log('Bar ticks'); }; var f = new Foo(1); f.tick(); // Foo ticks f.tock(); // Foo tocks console.log(f); // Foo { a=1, ... } var b = new Bar(1, 2); b.tick(); // Bar ticks b.tock(); // Foo tocks console.log(b); // Bar { a=1, b=2, ... }