a.js

function walk (x, y) {
  var path = [{}, {}];
  var player = document.querySelector('#player');

  var i = 0;
  var interval = setInterval(() => {
    var cords = path.splice(i, 1);
    player.setX(cords.x)
    player.setY(coords.y)
    i++;
  }, 500)

  return {
    stop: interval
  }
}


var stop = walk();
stop();

function gather (doSomething) {
  // var stopWalk = walk(x, y);
  // var stopChopDown = chopDown();
  // var stopReturn = walk(x, y);

  var w = walk(x, y);
  var stop = w.stop;

  w
  .then(function () {
    stop = chopDown();
  }).then(function () {
    walk(x, y)
  })

  return {
    stop,
  }
}

gather.stop()

b.js

var tasks = []

player.on('walk', (x, y) => {
  tasks.push(generateWalkTasks(x, y))
})

player.on('gather', (obj) => {
  tasks.push()
})

setInterval(() => {

}, 500)

player.on('fight', (opponent) => {
  tasks.push(
    generateFightTasks.bind(opponent)
  );
})