‘Ruby times method’ in JavaScript

times.js

// Ruby = 5.times { |i| puts i }
// JS   = (1).times(function(i){console.log(i);})
Number.prototype.times = function(cb) {
  var i = -1;

  while (++i < this) {
    cb(i);
  }

  return +this;
}

what is the purpose of returning +this?