使用Object.create实现类式继承

下面是官网的一个例子

//Shape - superclassfunction Shape() {  this.x = 0;  this.y = 0;}Shape.prototype.move = function(x, y) {    this.x += x;    this.y += y;    console.info("Shape moved.");};// Rectangle - subclassfunction Rectangle() {  Shape.call(this); //call super constructor.}Rectangle.prototype = Object.create(Shape.prototype);var rect = new Rectangle();rect instanceof Rectangle //true.rect instanceof Shape //true.rect.move(1, 1); //Outputs, "Shape moved."

此时Rectangle原型的constructor指向父类，如需要使用自身的构造，手动指定即可，如下

Rectangle.prototype.constructor = Rectangle;

使用utilities工具包自带的util.inherites

语法

util.inherits(constructor, superConstructor)

例子

const util = require('util');const EventEmitter = require('events');function MyStream() {    EventEmitter.call(this);}util.inherits(MyStream, EventEmitter);MyStream.prototype.write = function(data) {    this.emit('data', data);}var stream = new MyStream();console.log(stream instanceof EventEmitter); // trueconsole.log(MyStream.super_ === EventEmitter); // truestream.on('data', (data) => {  console.log(`Received data: "${data}"`);})stream.write('It works!'); // Received data: "It works!"

也很简单的例子，其实源码用了ES6的新特性，我们瞅一瞅

exports.inherits = function(ctor, superCtor) {  if (ctor === undefined || ctor === null)    throw new TypeError('The constructor to "inherits" must not be ' +                        'null or undefined');  if (superCtor === undefined || superCtor === null)    throw new TypeError('The super constructor to "inherits" must not ' +                        'be null or undefined');  if (superCtor.prototype === undefined)    throw new TypeError('The super constructor to "inherits" must ' +                        'have a prototype');  ctor.super_ = superCtor;  Object.setPrototypeOf(ctor.prototype, superCtor.prototype);};

其中Object.setPrototypeOf即为ES6新特性，将一个指定的对象的原型设置为另一个对象或者null

语法

Object.setPrototypeOf(obj, prototype)

obj为将要被设置原型的一个对象

如果设置成null,即为如下示例

Object.setPrototypeOf({}, null);

感觉setPrototypeOf真是人如其名啊，专门搞prototype来玩。

Object.setPrototypeOf = Object.setPrototypeOf || function (obj, proto) {  obj.__proto__ = proto;  return obj; }

即把proto赋给obj.__proto__就好了。

使用extends关键字

熟悉java的同学应该非常熟悉这个关键字，java中的继承都是靠它实现的。

使用extends修改之前util.inherits的例子，将会更简单

const EventEmitter = require('events');class MyEmitter extends EventEmitter {}const myEmitter = new MyEmitter();myEmitter.on('event', function() {  console.log('an event occurred!');});myEmitter.emit('event');

在下面的例子，定义了一个名为Polygon的类，然后定义了一个继承于Polygon的类 Square。注意到在构造器使用的 super()，supper()只能在构造器中使用，super函数一定要在this可以使用之前调用。

class Polygon {  constructor(height, width) {    this.name = 'Polygon';    this.height = height;    this.width = width;  }}class Square extends Polygon {  constructor(length) {    super(length, length);    this.name = 'Square';  }}

使用关键字后就不用婆婆妈妈各种设置原型了，关键字已经封装好了，很快捷方便。