xxerror v1.0.3

xxerror

custom error

用babel将es6中的error继承转换成es5代码时,

// es6
class CustomError extends Error {
}

// es5
"use strict";

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 CustomError = (function(_Error) {
  _inherits(CustomError, _Error);

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

    return _possibleConstructorReturn(
      this,
      (CustomError.__proto__ || Object.getPrototypeOf(CustomError)).apply(
        this,
        arguments
      )
    );
  }

  return CustomError;
})(Error);

我们可以看到在

    return _possibleConstructorReturn(
      this,
      (CustomError.__proto__ || Object.getPrototypeOf(CustomError)).apply(
        this,
        arguments
      )
    );

中CustomError.__proto__为Error,当我们对Error.apply(this, arguments)时，返回的是Error的实例而不是我们期望的CustomError的实例。这是因为Error被设计成可以通过new Error('message')，也可以通过Error('message')来实例化，而在我们的new CustomError()中，返回的是Error。