如何在JavaScript中为DOM元素创建自定义事件

本文概述

听事件
调度自定义事件
Polyfill

Javascript事件是JS生态系统的重要组成部分, 因为它们使我们能够知道事件何时发生而不会影响浏览器的性能。
你可以使用CustomEvent API创建自己的事件, 以便像通常对现有事件那样使用事件侦听器对这些事件做出反应。
听事件当我们要使用CustomEvent API调度事件时, 我们需要先监听它, 否则我们将永远不会得到任何结果。
请记住, 事件只能在DOM元素(文档, 输入, 按钮, div等)上调度。在这种情况下, 该事件将被命名为” OurSuperEvent” , 并且将在下一步中将其调度到文档上, 因此也将为该文档添加侦听器。

var element = document; // or // var element = document.getElementById("aRandomId"); element.addEventListener("OurSuperEvent", function (e) {// This is the information that we receive from the CustomEventconsole.log("The custom data of the event is : ", e.detail); // The event as itself (object with properties like {srcElement, isTrusted, target, defaultPrevent etc})console.log("Event is : ", e); }, false);

事件的detail属性包含调度事件时发送的信息。
注意：如前所述, 事件侦听器已添加到document元素。因此, 该事件也需要在document元素中调度, 否则该事件将永远不会被监听, 因为它不是我们为此事件分配的元素。
调度自定义事件现在我们有了一个侦听器, 可以告诉我们事件何时发生, 你需要学习如何调度它。
在侦听器中, 我们将侦听器附加到文档, 因此我们的事件(为了被侦听)也将在文档中调度。

var myData = http://www.srcmini.com/{id: 1, name:"An imaginary name", customProperty:"I need to know this string when the event is dispatched", moreData: [1, 2, 4, 5, 6, 7]}; var element = document; // or // var element = document.getElementById("aRandomId"); // The custom event that receives as first parameter the name of the type of the dispatchedEventvar event = new CustomEvent("OurSuperEvent", { detail: myData }); element.dispatchEvent(event);

如你所见, 自定义事件的实现非常简单, 简约和简洁。
但是(在Java语言世界中始终如此), 某些浏览器(Internet Explorer)没有实现相同的初始化。
当浏览器中存在window.CustomEvent对象时, 不能将其称为构造函数。代替新的CustomEvent(… ), 必须使用event = document.createEvent(‘ CustomEvent’ ), 然后使用event.initCustomEvent(… ), 如以下示例所示：

var myData = http://www.srcmini.com/{id: 1, name:"An imaginary name", customProperty:"I need to know this string when the event is dispatched", moreData: [1, 2, 4, 5, 6, 7]}; var element = document; // or // var element = document.getElementById("aRandomId"); //Dispatch an eventvar event = document.createEvent("CustomEvent"); event.initCustomEvent("OurSuperEvent", true, true, myData); element.dispatchEvent(event);

Polyfill请注意, 某些版本的Android旧的基于WebKit的WebView不支持CustomEvent API。幸运的是, 此功能有一个polyfill。
此摘要涵盖了事件IE6。该脚本可填充addEventListener, removeEventListener, dispatchEvent, CustomEvent和DOMContentLoaded。压缩并压缩后不到一半千字节。
你可以在此处访问存储库并查看源代码, 或直接在此处获取polyfill：

// EventListener | CC0 | github.com/jonathantneal/EventListenerthis.Element & & Element.prototype.attachEvent & & !Element.prototype.addEventListener & & (function () { function addToPrototype(name, method) {Window.prototype[name] = HTMLDocument.prototype[name] = Element.prototype[name] = method; } // add addToPrototype("addEventListener", function (type, listener) {vartarget = this, listeners = target.addEventListener.listeners = target.addEventListener.listeners || {}, typeListeners = listeners[type] = listeners[type] || []; // if no events exist, attach the listenerif (!typeListeners.length) {target.attachEvent("on" + type, typeListeners.event = function (event) {var documentElement = target.document & & target.document.documentElement || target.documentElement || { scrollLeft: 0, scrollTop: 0 }; // polyfill w3c properties and methodsevent.currentTarget = target; event.pageX = event.clientX + documentElement.scrollLeft; event.pageY = event.clientY + documentElement.scrollTop; event.preventDefault = function () { event.returnValue = http://www.srcmini.com/false }; event.relatedTarget = event.fromElement || null; event.stopImmediatePropagation = function () { immediatePropagation = false; event.cancelBubble = true }; event.stopPropagation = function () { event.cancelBubble = true }; event.target = event.srcElement || target; event.timeStamp = +new Date; var plainEvt = {}; for (var i in event) {plainEvt[i] = event[i]; }// create an cached list of the master events list (to protect this loop from breaking when an event is removed)for (var i = 0, typeListenersCache = [].concat(typeListeners), typeListenerCache, immediatePropagation = true; immediatePropagation & & (typeListenerCache = typeListenersCache[i]); ++i) {// check to see if the cached event still exists in the master events listfor (var ii = 0, typeListener; typeListener = typeListeners[ii]; ++ii) {if (typeListener == typeListenerCache) {typeListener.call(target, plainEvt); break; }}}}); }// add the event to the master event listtypeListeners.push(listener); }); // remove addToPrototype("removeEventListener", function (type, listener) {vartarget = this, listeners = target.addEventListener.listeners = target.addEventListener.listeners || {}, typeListeners = listeners[type] = listeners[type] || []; // remove the newest matching event from the master event listfor (var i = typeListeners.length - 1, typeListener; typeListener = typeListeners[i]; --i) {if (typeListener == listener) {typeListeners.splice(i, 1); break; }}// if no events exist, detach the listenerif (!typeListeners.length & & typeListeners.event) {target.detachEvent("on" + type, typeListeners.event); } }); // dispatch addToPrototype("dispatchEvent", function (eventObject) {vartarget = this, type = eventObject.type, listeners = target.addEventListener.listeners = target.addEventListener.listeners || {}, typeListeners = listeners[type] = listeners[type] || []; try {return target.fireEvent("on" + type, eventObject); } catch (error) {if (typeListeners.event) {typeListeners.event(eventObject); }return; } }); // CustomEvent Object.defineProperty(Window.prototype, "CustomEvent", {get: function () {var self = this; return function CustomEvent(type, eventInitDict) {var event = self.document.createEventObject(), key; event.type = type; for (key in eventInitDict) {if (key == 'cancelable'){event.returnValue = http://www.srcmini.com/!eventInitDict.cancelable; } else if (key =='bubbles'){event.cancelBubble = !eventInitDict.bubbles; } else if (key == 'detail'){event.detail = eventInitDict.detail; }}return event; }; } }); // ready function ready(event) {if (ready.interval & & document.body) {ready.interval = clearInterval(ready.interval); document.dispatchEvent(new CustomEvent("DOMContentLoaded")); } } ready.interval = setInterval(ready, 1); window.addEventListener("load", ready); })(); (!this.CustomEvent || typeof this.CustomEvent === "object") & & (function() { // CustomEvent for browsers which don't natively support the Constructor method this.CustomEvent = function CustomEvent(type, eventInitDict) {var event; eventInitDict = eventInitDict || {bubbles: false, cancelable: false, detail: undefined}; try {event = document.createEvent('CustomEvent'); event.initCustomEvent(type, eventInitDict.bubbles, eventInitDict.cancelable, eventInitDict.detail); } catch (error) {// for browsers which don't support CustomEvent at all, we use a regular event insteadevent = document.createEvent('Event'); event.initEvent(type, eventInitDict.bubbles, eventInitDict.cancelable); event.detail = eventInitDict.detail; }return event; }; })();

【如何在JavaScript中为DOM元素创建自定义事件】玩得开心！