Simplyfied the code. Ready to rebuild on top of.

Room.js

@@ -0,0 +1,17 @@
+module.exports = {
+	setup: function () { Room.prototype = _Room.prototype; }
+}
+
+class _Room extends Room {
+	begin(){}
+
+	tick(){
+		const creepsCount = this.find(FIND_MY_CREEPS).length;
+		console.log(creepsCount);
+		if(creepsCount < 5){
+			const spawn = this.find(FIND_MY_STRUCTURES, {filter: {structureType: STRUCTURE_SPAWN}})[0];
+			spawn.createHarvester();
+		}
+	}
+}   
+