docs: function arraysEqual(first, second){
      if(!Array.isArray(first)) throw new Error("first must be an array.");    
      if(!Array.isArray(second)) throw new Error("second must be an array.");
      if(first.length !== second.length) return false;
      for (var i = 0; i < first.length; i++) {
          if(first[i] !== second[i]) return false;
      }
      return true;
  }