如何使用 JavaScript EventTarget? [英] How to use JavaScript EventTarget?

问题描述

我想在我的客户端程序中创建一个自定义事件发射器.我正在为 EventTarget

I would like to create a custom event emitter in my client-side programs. I am referencing this (sparse) documentation for EventTarget

我的实施尝试

var Emitter = function Emitter() {
  EventTarget.call(this);
};

Emitter.prototype = Object.create(EventTarget.prototype, {
  constructor: {
    value: Emitter
  }
});

我想要的用途

var e = new Emitter();

e.addEventListener("hello", function() {
  console.log("hello there!");
});

e.dispatchEvent(new Event("hello"));
// "hello there!"

失败的地方

var e = new Emitter();
// TypeError: Illegal constructor

我做错了什么?

更新

以下是可能的，但它是一个依赖于虚拟 DOMElement 的 hack

The following is possible, but it's a hack that depends on a dummy DOMElement

var fake = document.createElement("phony");
fake.addEventListener("hello", function() { console.log("hello there!"); });
fake.dispatchEvent(new Event("hello"));
// "hello there!"

我想知道如何在不使用虚拟元素的情况下做到这一点

I'd like to know how to do this without having to use the dummy element

推荐答案

我之前放弃了这个，但最近又需要它.这是我最终使用的.

I gave up on this awhile ago, but recently needed it again. Here's what I ended up using.

ES6

class Emitter {
  constructor() {
    var delegate = document.createDocumentFragment();
    [
      'addEventListener',
      'dispatchEvent',
      'removeEventListener'
    ].forEach(f =>
      this[f] = (...xs) => delegate[f](...xs)
    )
  }
}

// sample class to use Emitter
class Example extends Emitter {}

// run it
var e = new Example()
e.addEventListener('something', event => console.log(event))
e.dispatchEvent(new Event('something'))

ES5

function Emitter() {
  var eventTarget = document.createDocumentFragment()

  function delegate(method) {
    this[method] = eventTarget[method].bind(eventTarget)
  }

  [
    "addEventListener",
    "dispatchEvent",
    "removeEventListener"
  ].forEach(delegate, this)
}

// sample class to use it
function Example() {
  Emitter.call(this)
}

// run it
var e = new Example()

e.addEventListener("something", function(event) {
  console.log(event)
})

e.dispatchEvent(new Event("something"))

是的！

对于那些需要支持旧版本 ecmascript 的人，这里是你

For those that need to support older versions of ecmascript, here you go

// IE < 9 compatible
function Emitter() {
  var eventTarget = document.createDocumentFragment();

  function addEventListener(type, listener, useCapture, wantsUntrusted) {
    return eventTarget.addEventListener(type, listener, useCapture, wantsUntrusted);
  }

  function dispatchEvent(event) {
    return eventTarget.dispatchEvent(event);
  }

  function removeEventListener(type, listener, useCapture) {
    return eventTarget.removeEventListener(type, listener, useCapture);
  }

  this.addEventListener = addEventListener;
  this.dispatchEvent = dispatchEvent;
  this.removeEventListener = removeEventListener;
}

用法保持不变

这篇关于如何使用 JavaScript EventTarget?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！