babeljs不能正确地转换扩展类

Question

我从MDN获得了这个示例代码(稍微修改以打印结果)：

​

"use strict";

class myDate extends Date {
  constructor() {
    super();
  }

  getFormattedDate() {
    var months = ['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'];
    return this.getDate() + "-" + months[this.getMonth()] + "-" + this.getFullYear();
  }
}

var testDate = new myDate();
document.write(testDate.getFormattedDate());

​

它可以在Google浏览器和node5上工作，但是当我使用babeljs传输到ES5 (ES2015预设)时，它就不起作用了：

​

"use strict";

var _createClass = function () { function defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } } return function (Constructor, protoProps, staticProps) { if (protoProps) defineProperties(Constructor.prototype, protoProps); if (staticProps) defineProperties(Constructor, staticProps); return Constructor; }; }();

function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }

function _possibleConstructorReturn(self, call) { if (!self) { throw new ReferenceError("this hasn't been initialised - super() hasn't been called"); } return call && (typeof call === "object" || typeof call === "function") ? call : self; }

function _inherits(subClass, superClass) { if (typeof superClass !== "function" && superClass !== null) { throw new TypeError("Super expression must either be null or a function, not " + typeof superClass); } subClass.prototype = Object.create(superClass && superClass.prototype, { constructor: { value: subClass, enumerable: false, writable: true, configurable: true } }); if (superClass) Object.setPrototypeOf ? Object.setPrototypeOf(subClass, superClass) : subClass.__proto__ = superClass; }

var myDate = function (_Date) {
  _inherits(myDate, _Date);

  function myDate() {
    _classCallCheck(this, myDate);

    return _possibleConstructorReturn(this, Object.getPrototypeOf(myDate).call(this));
  }

  _createClass(myDate, [{
    key: 'getFormattedDate',
    value: function getFormattedDate() {
      var months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
      return this.getDate() + "-" + months[this.getMonth()] + "-" + this.getFullYear();
    }
  }]);

  return myDate;
}(Date);

var testDate = new myDate();
document.write(testDate.getFormattedDate());

​

为什么？

我在巴贝尔博士上找到了答案

部分支撑 内置子类的可分类性应该根据具体情况进行评估，因为类(如HTMLElement )可以被子类化，而许多类(如日期、数组和错误)不能由于ES5引擎的限制而产生。

如果babel在看到本地对象扩展(它不支持)时抛出一个错误，而不是假装一切都是美好的，并产生错误的代码，我会很感激。

Answer 1

根据ECMAScript 6兼容性表的说法，BabelJS不支持类扩展。