code: function range(begin, end) {
    var interval = arguments.length <= 2 || arguments[2] === undefined ? 1 : arguments[2];
  
    var a = [];
  
    for (var i = begin; i < begin + end; i += interval) {
      a.push(i);
    }
  
    return a;
  }
docs: infinite range generator will run as fast as the data access allows.