我通常附加一个类到元素，然后检查类是否存在，像这样:

let element = document.getElementsById("someElement");

if(!element.classList.contains('attached-listener'))
   element.addEventListener("click", this.itemClicked);

element.classList.add('attached-listener');

下面是我用来检查是否存在动态附加事件侦听器的脚本。我使用jQuery附加一个事件处理程序到一个元素，然后触发该事件(在本例中是'click'事件)。通过这种方式，我可以检索和捕获仅在附加事件处理程序时才存在的事件属性。

var eventHandlerType;

$('#contentDiv').on('click', clickEventHandler).triggerHandler('click');

function clickEventHandler(e) {
    eventHandlerType = e.type;
}

if (eventHandlerType === 'click') {
    console.log('EventHandler "click" has been applied');
}

我写了一个Chrome扩展，需要确定页面上的哪些元素响应点击。我是这样做的:

(1)舱单。Json，设置“run_at”属性为“document_start”。(我们需要在页面开始运行之前注入一个脚本。)

(2)在你的内容脚本中，添加一段代码注入一个脚本到页面中，该脚本将覆盖EventTarget.prototype.addEventListener来标记所有动态分配点击监听器的元素:

let flagClickHandledElements = function() {
    let oldEventListener = EventTarget.prototype.addEventListener;
    EventTarget.prototype.addEventListener = function(event_name, handler_func) {
        if (event_name === 'click') {
            if (this.setAttribute) {
                this.setAttribute('data-has_click_handler', true);
            }
        }
        if (oldEventListener)
            oldEventListener(event_name, handler_func);
    }
}

function injectScript(func) {
    let codeString = '(' + func + ')();';
    let script = document.createElement('script');
    script.textContent = codeString;
    (document.head||document.documentElement).appendChild(script);
}

injectScript(flagClickHandledElements);

(3)将“webNavigation”添加到manifest.json中的“permissions”列表中

(4)在后台脚本中添加一些代码，当页面加载完成时通知内容脚本:

function onPageDoneLoading(details)
{
    chrome.tabs.sendMessage(details.tabId, {"action": "doneloading"});
}

chrome.webNavigation.onCompleted.addListener(onPageDoneLoading);

(5)当页面加载完成时，让你的内容脚本注入另一个脚本到页面中，扫描页面上的所有元素，寻找老式的“onclick”处理程序:

let gatherOldStyleClickHandledElements = function() {
    let all_elements = document.getElementsByTagName("*");
    for (let i = 0; i < all_elements.length; i++) {
        let el = all_elements[i];
        if (el.setAttribute && el.onclick) {
            el.setAttribute('data-has_click_handler', true);
        }
    }
}

function onReceiveMessage(request) {
    if (request.action === 'doneloading') {
        injectScript(gatherOldStyleClickHandledElements);
    } else {
        console.log('Unrecognized message');
    }

    return Promise.resolve("Dummy response to keep the console quiet");
}

(6)最后，你可以在你的内容脚本中测试一个元素，看看它是否有一个像这样的点击处理程序:

if (el.getAttribute('data-has_click_handler'))
    console.log('yep, this element has a click handler');

我写了3个函数来做这个:

var addEvent = function(object, type, callback)
{
    if (object != null && typeof(object) != 'undefined' && object.addEventListener)
    {
        object.isAttached = typeof object.isAttached == "undefined" ? [] : object.isAttached;
        if (!object.isAttached[type])
        {
            object.isAttached[type] = true;
            object.addEventListener(type, callback, false);
        }
    }
};

var removeEvent = function(object, type, callback)
{
    if (object != null && typeof(object) != "undefined" && typeof object.isAttached != "undefined" && object.isAttached[type])
    {
        object.removeEventListener(type, callback, false);
        object.isAttached[type] = false;
    }
};

var hasEvent = function(object, type, callback)
{
    return object != null && typeof(object) != "undefined" && typeof object.isAttached != "undefined" && object.isAttached[type];
};

函数的使用很简单:

function mousemove(e)
{
    console.log("x:" + e.clientX + ", y:" + e.clientY);
}

if (hasEvent(window, "mousemove", mousemove))
    console.log('window has "mousemove" event with "mousemove" callback');
else
    console.log('window does not have "mousemove" event with "mousemove" callback');

addEvent(window, "mousemove", mousemove);

if (hasEvent(window, "mousemove", mousemove))
    console.log('window has "mousemove" event with "mousemove" callback');
else
    console.log('window does not have "mousemove" event with "mousemove" callback');
/*
Output
window does not have "mousemove" event with "mousemove"
window has "mousemove" event with "mousemove" callback
The x and y coordinates of mouse as you move it
*/

2022年更新:

我在TypeScript中编写了实用工具方法，根据这个答案附加和分离事件，但这个答案是正确的。希望有人觉得有用。

export const attachEvent = (
  element: Element,
  eventName: string,
  callback: () => void
) => {
  if (element && eventName && element.getAttribute('listener') !== 'true') {
    element.setAttribute('listener', 'true');
    element.addEventListener(eventName, () => {
      callback();
    });
  }
};

export const detachEvent = (
  element: Element,
  eventName: string,
  callback: () => void
) => {
  if (eventName && element) {
    element.removeEventListener(eventName, callback);
  }
};

导入并像这样在任何地方使用它

  attachEvent(domElement, 'click', this.myfunction.bind(this));
  detachEvent(domElement, 'click', this.myfunction);

我是这样做的:

const element = document.getElementById('div');

if (element.getAttribute('listener') !== 'true') {
     element.addEventListener('click', function (e) {
         const elementClicked = e.target;
         elementClicked.setAttribute('listener', 'true');
         console.log('event has been attached');
    });
}

在附加侦听器时为元素创建一个特殊属性，然后检查它是否存在。