源码分析

/**
 * 用于检查构造函数中super()是否被正确调用,然后产生构造函数的返回值
 * 它(与传到call参数上的超类构造函数调用)完成了构造函数的super功能
 * @param self 通常传入子类构造函数的this
 * @param call 通常传入一个超类构造函数在子类this上的调用结果
 */
function _possibleConstructorReturn(self, call) {
  // 检查子类的this是否存在
  if (!self) {
    throw new ReferenceError("this hasn't been initialised - super() hasn't been called");
  }
  // 检查超类构造函数在子类this上的调用结果是否是类假值\object\function,如果是则返回这个值,如果不是则返回原来子类的this
  return call && (typeof call === "object" || typeof call === "function") ? call : self;
}

例子

var Animal = function () {
  function Animal(weight) {
    _classCallCheck(this, Animal);

    this.weight = weight;
  }

  Animal.prototype.bite = function bite() {};

  return Animal;
}();

var Person = function (_Animal) {
  _inherits(Person, _Animal);

  function Person(weight, phone) {
    _classCallCheck(this, Person);

    var _this = _possibleConstructorReturn(this, _Animal.call(this, weight));

    _this.phone = phone;
    return _this;
  }

  Person.prototype.think = function think() {};

  return Person;
}(Animal);

var tom = new Person();

其中_possibleConstructorReturn所在的那一行完成了ES6中的super()功能。即super(weight);

分类: babel

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