Improvement of JS date compare

date.compare.js

(function () {
  "use strict";

  /**
   * Compare dates.
   * @param {Date|String} date instance or string in W3C format
   * @throws TypeError
   * @return {int} 0 = equals, -1 = gt, 1 = lt
   */
  Date.prototype.compare = function (date) {
    if (! (date instanceof Date)) {
      date = new Date(date);
    }

    if (date.toString() === "Invalid Date") {
      throw TypeError();
    }

    return (+this > +date)-(+this < +date);
  };
})();

var date = new Date('2015-02-04');
console.log(date.compare('2015-02-04')); // 0
console.log(date.compare('2015-02-10')); // -1
console.log(date.compare('2015-02-01')); // 1