Node.js - 从模块发出事件的最佳方法

Question

我一直在玩EventEmitter,但我对如何从模块中实现它感到困惑.我见过几种不同的方式,它们似乎都有效.以下是我见过的一些内容:

从这里:

var Twitter = function() {...};

Twitter.prototype = new events.EventEmitter;

但是在"掌握节点"中他们这样做:

function Dog(name) {
  this.name = name;
  EventEmitter.call(this);
}

Dog.prototype.__proto__ = EventEmitter.prototype;

(为什么你需要.call它？)

然后在我自己的代码中我尝试了另一种方式:

function Class() {}

Class.prototype = EventEmitter.prototype;

它们都是以自己的方式继承EventEmitter,所以最简单的解决方案不是最好的吗？

Answer 1

Node有一个库函数util.inherits,它比接受的答案稍微简单一些.以下代码是从v0.8.12文档修改的.

var util = require("util");
var events = require("events");

function MyStream() {
  events.EventEmitter.call(this);
}

util.inherits(MyStream, events.EventEmitter);

Answer 2

你应该使用__proto__继承的风格.这假设您仅为Node编码,或仅支持您喜欢的浏览器.此外,Base.call(this)如果您关心基础原型的构造函数中的任何逻辑,则是必要的.

__proto__引用基础原型的技术将确保instanceof操作员正确识别原型的实例..constructor子类的实例的属性将引用您期望它的构造函数.它还具有不实例化基本原型的新实例的好处.

该new Base()样式还将确保instanceof为您提供正确的答案,但它将运行Base的构造函数.通常不是问题,但如果您的基础构造函数具有必需参数,则可能会出现问题.它还将.constructor属性设置为基础构造函数,而不是后代构造函数.

将类的原型设置为基类的原型将会混淆,instanceof因为基类的任何后代也将显示为子类的实例.

清楚如泥,对吗？这个例子应该有帮助:

// Base constructor.
// A, B, and C will inherit from Base.
function Base() {
    this.name = 'base';
}

// new Base() style
function A() {
    Base.call(this);
}
A.prototype = new Base();

// __proto__ = prototype style
function B() {
    Base.call(this);
}
B.prototype.__proto__ = Base.prototype;

// prototype = protoype style
function C() {
    Base.call(this);
}
C.prototype = Base.prototype;

// create instances
var a = new A();
var b = new B();
var c = new C();

// are we who we think we are?
console.assert(a instanceof A);
console.assert(b instanceof B);
console.assert(c instanceof C);
// so far so good

// do we respect our elders?
console.assert(a instanceof Base);
console.assert(b instanceof Base);
console.assert(c instanceof Base);
// we have respect

// test to see that Base.call(this)
// functioned as expected
console.assert(a.name == 'base');
console.assert(b.name == 'base');
console.assert(c.name == 'base');
// ok, good...

// but now things get weird
console.assert(a instanceof C);
console.assert(b instanceof C);
// that's not right! a is not C, b is not C!

// At least A and B do not confuse identities
console.assert(!(a instanceof B));
console.assert(!(b instanceof A));

console.assert(!(c instanceof A));
console.assert(!(c instanceof B));

// so we've determined that style C is no good.
// C confuses the inheritance chain.

// B is the winner.

// Why? Only B passes this test
console.assert(b.constructor == B);

// a and c's constructors actually point to the Base constructor
console.assert(a.constructor == Base);
console.assert(c.constructor == Base);

// Word B.