我做了这样的事情：

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');
    });
}

附加侦听器时为元素创建特殊属性，然后检查它是否存在。

没有办法检查动态附加的事件侦听器是否存在。

查看是否附加了事件侦听器的唯一方法是像这样附加事件侦听器：

elem.onclick = function () { console.log (1) }

然后，您可以onclick通过返回!!elem.onclick（或类似的东西）来测试是否附加了事件侦听器。

我会做的是在您的函数之外创建一个布尔值，该布尔值以 FALSE 开始，并在您附加事件时设置为 TRUE。在您再次附加事件之前，这将为您提供某种标志。这是这个想法的一个例子。

// initial load
var attached = false;

// this will only execute code once
doSomething = function()
{
 if (!attached)
 {
  attached = true;
  //code
 }
} 

//attach your function with change event
window.onload = function()
{
 var txtbox = document.getElementById('textboxID');

 if (window.addEventListener)
 {
  txtbox.addEventListener('change', doSomething, false);
 }
 else if(window.attachEvent)
 {
  txtbox.attachEvent('onchange', doSomething);
 }
}

可能的重复：检查元素上是否有事件侦听器。没有 jQuery 请在那里找到我的答案。

基本上这里是 Chromium (Chrome) 浏览器的技巧：

getEventListeners(document.querySelector('your-element-selector'));

tl;dr：不，您不能以任何本机支持的方式执行此操作。

我知道实现这一目标的唯一方法是创建一个自定义存储对象，您可以在其中记录添加的侦听器。大致如下：

/* Create a storage object. */
var CustomEventStorage = [];

第 1 步：首先，您需要一个可以遍历存储对象并返回给定元素（或 false）的元素记录的函数。

/* The function that finds a record in the storage by a given element. */
function findRecordByElement (element) {
    /* Iterate over every entry in the storage object. */
    for (var index = 0, length = CustomEventStorage.length; index < length; index++) {
        /* Cache the record. */
        var record = CustomEventStorage[index];

        /* Check whether the given element exists. */
        if (element == record.element) {
            /* Return the record. */
            return record;
        }
    }

    /* Return false by default. */
    return false;
}

第 2 步：然后，您将需要一个可以添加事件侦听器但也可以将侦听器插入存储对象的函数。

/* The function that adds an event listener, while storing it in the storage object. */
function insertListener (element, event, listener, options) {
    /* Use the element given to retrieve the record. */
    var record = findRecordByElement(element);

    /* Check whether any record was found. */
    if (record) {
        /* Normalise the event of the listeners object, in case it doesn't exist. */
        record.listeners[event] = record.listeners[event] || [];
    }
    else {
        /* Create an object to insert into the storage object. */
        record = {
            element: element,
            listeners: {}
        };

        /* Create an array for event in the record. */
        record.listeners[event] = [];

        /* Insert the record in the storage. */
        CustomEventStorage.push(record);
    }

    /* Insert the listener to the event array. */
    record.listeners[event].push(listener);

    /* Add the event listener to the element. */
    element.addEventListener(event, listener, options);
}

步骤3：根据您的问题的实际需求，您将需要以下函数来检查元素是否已添加指定事件的事件侦听器。

/* The function that checks whether an event listener is set for a given event. */
function listenerExists (element, event, listener) {
    /* Use the element given to retrieve the record. */
    var record = findRecordByElement(element);

    /* Check whether a record was found & if an event array exists for the given event. */
    if (record && event in record.listeners) {
        /* Return whether the given listener exists. */
        return !!~record.listeners[event].indexOf(listener);
    }

    /* Return false by default. */
    return false;
}

第 4 步：最后，您将需要一个可以从存储对象中删除侦听器的函数。

/* The function that removes a listener from a given element & its storage record. */
function removeListener (element, event, listener, options) {
    /* Use the element given to retrieve the record. */
    var record = findRecordByElement(element);

    /* Check whether any record was found and, if found, whether the event exists. */
    if (record && event in record.listeners) {
        /* Cache the index of the listener inside the event array. */
        var index = record.listeners[event].indexOf(listener);

        /* Check whether listener is not -1. */
        if (~index) {
            /* Delete the listener from the event array. */
            record.listeners[event].splice(index, 1);
        }

        /* Check whether the event array is empty or not. */
        if (!record.listeners[event].length) {
            /* Delete the event array. */
            delete record.listeners[event];
        }
    }

    /* Add the event listener to the element. */
    element.removeEventListener(event, listener, options);
}

片段：

window.onload = function () {
  var
    /* Cache the test element. */
    element = document.getElementById("test"),

    /* Create an event listener. */
    listener = function (e) {
      console.log(e.type + "triggered!");
    };

  /* Insert the listener to the element. */
  insertListener(element, "mouseover", listener);

  /* Log whether the listener exists. */
  console.log(listenerExists(element, "mouseover", listener));

  /* Remove the listener from the element. */
  removeListener(element, "mouseover", listener);

  /* Log whether the listener exists. */
  console.log(listenerExists(element, "mouseover", listener));
};

<!-- Include the Custom Event Storage file -->
<script src = "https://cdn.rawgit.com/angelpolitis/custom-event-storage/master/main.js"></script>

<!-- A Test HTML element -->
<div id = "test" style = "background:#000; height:50px; width: 50px"></div>

虽然自 OP 发布问题以来已经过去了 5 年多，但我相信将来偶然发现它的人会从这个答案中受益，因此请随时对其提出建议或改进。😊