en.javascript.info/1-js/4-object-basics/03-object-methods/8-chain-calls/_js.view/solution.js

let ladder = {
  step: 0,
  up: function() { 
    this.step++;
    return this;
  },
  down: function() { 
    this.step--;
    return this;
  },
  showStep: function() { 
    alert(this.step);
  }
};