screeps_main.js

module.exports.loop = function () {
    for (let name in Game.creeps) {
        let creep = Game.creeps[name];

        if (!creep.memory.sourceId) {

            var source = creep.pos.findClosestByPath(FIND_SOURCES_ACTIVE, {
                filter: (s) => s.pos.findInRange(FIND_MY_CREEPS, 1).length == 0
            });

            if (source) {
                creep.memory.sourceId = source.id;
            }
        }

        if (creep.memory.sourceId) {
            creepHarvestBehavior(creep, Game.getObjectById(creep.memory.sourceId), Game.spawns.Spawn1);
        }
    }

    if (!Game.spawns.Spawn1.spawning && Game.spawns.Spawn1.energy == 300) {
        Game.spawns.Spawn1.createCreep([WORK, CARRY, MOVE, MOVE]);
    }
}

function creepHarvestBehavior(creep, source, returnStructure) {
    if (_.sum(creep.carry) == creep.carryCapacity) {
        if (creep.transfer(returnStructure, RESOURCE_ENERGY) == ERR_NOT_IN_RANGE) {
            creep.moveTo(returnStructure);
        }
    }
    else {
        if (creep.harvest(source) == ERR_NOT_IN_RANGE) {
            creep.moveTo(source);
        }
    }
}