ES5和ES6的继承对比

ES5的继承实现，这里以最佳实践：寄生组合式继承方式来实现。（为什么是最佳实践，前面有随笔讲过了，可以参考）

function Super(name) { this.name = name; } Super.prototype.sayName = function() { console.log(this.name) } function Sub(name, age) { Super.call(this, name); this.age = age; } Sub.prototype.sayAge = function() { console.log(this.age) } Sub.prototype = Object.create(Super.prototype, { constructor: { value: Sub, writable: true, configurable: true } });

这里的Object.create可以替换成Object.setPrototypeOf，好处是不用再手动绑定constructor的指向。

这是ES5继承，再看下ES6的继承，同样实现上面的效果

class Super { constructor(name) { this.name = name; } sayName() { console.log(this.name); } } class Sub extends Super { constructor(name, age) { super(name); this.age = age; } sayAge() { console.log(this.age); } }

 很明显，ES6的继承要更简洁点，那区别是什么？

我们看一下babel解析后的ES6的继承：

"use strict"; function _typeof(obj) { if (typeof Symbol === "function" && typeof Symbol.iterator === "symbol") { _typeof = function _typeof(obj) { return typeof obj; }; } else { _typeof = function _typeof(obj) { return obj && typeof Symbol === "function" && obj.constructor === Symbol && obj !== Symbol.prototype ? "symbol" : typeof obj; }; } return _typeof(obj); } function _possibleConstructorReturn(self, call) { if (call && (_typeof(call) === "object" || typeof call === "function")) { return call; } return _assertThisInitialized(self); } function _assertThisInitialized(self) { if (self === void 0) { throw new ReferenceError("this hasn't been initialised - super() hasn't been called"); } return self; } function _getPrototypeOf(o) { _getPrototypeOf = Object.setPrototypeOf ? Object.getPrototypeOf : function _getPrototypeOf(o) { return o.__proto__ || Object.getPrototypeOf(o); }; return _getPrototypeOf(o); } function _inherits(subClass, superClass) { if (typeof superClass !== "function" && superClass !== null) { throw new TypeError("Super expression must either be null or a function"); } subClass.prototype = Object.create(superClass && superClass.prototype, { constructor: { value: subClass, writable: true, configurable: true } }); if (superClass) _setPrototypeOf(subClass, superClass); } function _setPrototypeOf(o, p) { _setPrototypeOf = Object.setPrototypeOf || function _setPrototypeOf(o, p) { o.__proto__ = p; return o; }; return _setPrototypeOf(o, p); } function _instanceof(left, right) { if (right != null && typeof Symbol !== "undefined" && right[Symbol.hasInstance]) { return !!right[Symbol.hasInstance](left); } else { return left instanceof right; } } function _classCallCheck(instance, Constructor) { if (!_instanceof(instance, Constructor)) { throw new TypeError("Cannot call a class as a 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); } } function _createClass(Constructor, protoProps, staticProps) { if (protoProps) _defineProperties(Constructor.prototype, protoProps); if (staticProps) _defineProperties(Constructor, staticProps); return Constructor; } var Super = /*#__PURE__*/ function () { function Super(name) { _classCallCheck(this, Super); this.name = name; } _createClass(Super, [{ key: "sayName", value: function sayName() { console.log(this.name); } }]); return Super; }(); var Sub = /*#__PURE__*/ function (_Super) { _inherits(Sub, _Super); function Sub(name, age) { var _this; _classCallCheck(this, Sub); _this = _possibleConstructorReturn(this, _getPrototypeOf(Sub).call(this, name)); _this.age = age; return _this; } _createClass(Sub, [{ key: "sayAge", value: function sayAge() { console.log(this.age); } }]); return Sub; }(Super);

 代码有点多，但很多都是做了一些类型检查或者是polify的兼容，关键的方法是_inherits

function _inherits(subClass, superClass) { if (typeof superClass !== "function" && superClass !== null) { throw new TypeError("Super expression must either be null or a function"); } subClass.prototype = Object.create(superClass && superClass.prototype, { constructor: { value: subClass, writable: true, configurable: true } }); if (superClass) _setPrototypeOf(subClass, superClass); }

前面的和ES5继承没有区别，也是用了Object.create实现子类的prototype继承父类的prototype，但是最后多了一个操作

_setPrototypeOf(subClass, superClass);

 看一下对应的函数定义

function _setPrototypeOf(o, p) { _setPrototypeOf = Object.setPrototypeOf || function _setPrototypeOf(o, p) { o.__proto__ = p; return o; }; return _setPrototypeOf(o, p); }

 意图很明显了，就是为了实现子类继承父类！

从这里我们看出差别了，ES6的继承除了子类的原型继承以外，还多了子类的自身继承父类，但是为什么这么做呢？

 

 

 

 

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转载于:https://www.cnblogs.com/yanchenyu/p/11459334.html