向一个在javascript中还不存在的元素添加一个事件监听器
Adding an event listener to an element that doesn't exist yet in vanilla javascript
在JQuery中我可以这样做:
$(document).on("click","a.someBtn",function(e){
console.log("hi");
});
向尚不存在的元素添加事件侦听器。我似乎无法弄清楚如何将事件侦听器添加到在普通javascript中尚未存在的元素中。
下面的代码显然不能工作:
query.addEventListener( "click", someListener );
编辑
我想做的是通过查询选择器比较项。我选择的是querySelectorAll
中还不存在的元素。它比仅仅检查标记名称要动态一些。
使用event
对象中的target属性来获取被单击的元素。然后,手动测试类型/attributes/ids
document.addEventListener( "click", someListener );
function someListener(event){
var element = event.target;
if(element.tagName == 'A' && element.classList.contains("someBtn")){
console.log("hi");
}
}
您可以使用event.target
<发送事件的对象的引用。
代码/em>
(function () {
"use strict";
document.getElementsByTagName('body')[0].addEventListener('click', function(e) {
if (e.target.tagName == 'A' && e.target.classList.contains("someBtn")) {
alert('Clicked');
}
}, false);
})();
(function() {
"use strict";
var a = document.createElement('a');
a.textContent = 'Click Me';
a.href = '#';
document.body.appendChild(a);
document.getElementsByTagName('body')[0].addEventListener('click', function(e) {
if (e.target.tagName == 'A') {
alert('Clicked');
}
}, false);
})();
您需要使用DOM MutationObserver Events来应用addEventListener。自2012年以来,我认为所有主要浏览器都可以使用这个DOM API。
我用这个来降低由他们的代码片段(https://www.w3schools.com/howto/howto_google_translate.asp)创建的谷歌翻译工具栏。由于它是动态创建元素(iframe),所以遇到的问题与您遇到的问题相同。只需根据需要更改回调函数和变量。
//Observer for Google translator bar creation and action to move to bottom
// Select the nodetree that will be observed for mutations
var nodetree = document.getElementsByTagName("body")[0];
// Select the target node atributes (CSS selector)
var targetNode = "iframe.goog-te-banner-frame";
// Options for the observer (which mutations to observe)
var config = { attributes: false, childList: true };
// Callback function to execute when mutations of DOM tree are observed
var lowerGoogleTranslateBar = function(mutations_on_DOMtree) {
for(var mutation of mutations_on_DOMtree) {
if (mutation.type == 'childList') {
console.log(mutation);
if (document.querySelector(targetNode) != null) {
//40px is the height of the bar
document.querySelector(targetNode).style.setProperty("top", "calc(100% - 40px)");
//after action is done, disconnect the observer from the nodetree
observerGoogleTranslator.disconnect();
}
}
}
};
// Create an observer instance linked to the callback function
var observerGoogleTranslator = new MutationObserver(lowerGoogleTranslateBar);
// Start observing the target node for configured mutations
observerGoogleTranslator.observe(nodetree, config);
您可以在这里了解更多信息:https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver
这是一个可以让你像jQuery的.on
一样添加"live"事件的函数。它可以像这样调用:
addLiveListener(scope, selector, event, function reference);
查看函数注释,了解每个参数的描述。
/**
* Adds a istener for specific tags for elements that may not yet
* exist.
* @param scope a reference to an element to look for elements in (i.e. document)
* @param selector the selector in form [tag].[class] (i.e. a.someBtn)
* @param event and event (i.e. click)
* @param funct a function reference to execute on an event
*/
function addLiveListener(scope, selector, event, funct) {
/**
* Set up interval to check for new items that do not
* have listeners yet. This will execute every 1/10 second and
* apply listeners to
*/
setInterval(function() {
var selectorParts = selector.split('.');
var tag = selectorParts.shift();
var className;
if (selectorParts.length)
className = selectorParts.shift();
if (tag != "") {
tag = tag.toUpperCase();
var elements = scope.getElementsByTagName(tag);
} else
var elements = scope.getElementsByClassName(className);
for (var i = 0; i < elements.length; i++) {
if (elements[i][event + '_processed'] === undefined && (tag == "" || elements[i].tagName == tag)) {
elements[i].addEventListener(event, funct);
}
}
}, 1000);
}
这里是一个完整的工作演示:
/**
* Adds another anchor with no events attached and lets
* our other code auto-attach events
*/
var currentAnchor = 3;
function addAnchor() {
currentAnchor++;
var element = document.createElement('a');
element.href = "#";
element.innerHTML = "Anchor " + currentAnchor;
element.className = "someBtn";
document.getElementById("holder").appendChild(element);
}
/**
* Adds a istener for specific tags for elements that may not yet
* exist.
* @param scope a reference to an element to look for elements in (i.e. document)
* @param selector the selector in form [tag].[class] (i.e. a.someBtn)
* @param event and event (i.e. click)
* @param funct a function reference to execute on an event
*/
function addLiveListener(scope, selector, event, funct) {
/**
* Set up interval to check for new items that do not
* have listeners yet. This will execute every 1/10 second and
* apply listeners to
*/
setInterval(function() {
var selectorParts = selector.split('.');
var tag = selectorParts.shift();
var className;
if (selectorParts.length)
className = selectorParts.shift();
if (tag != "") {
tag = tag.toUpperCase();
var elements = scope.getElementsByTagName(tag);
} else
var elements = scope.getElementsByClassName(className);
for (var i = 0; i < elements.length; i++) {
if (elements[i][event + '_processed'] === undefined && (tag == "" || elements[i].tagName == tag)) {
elements[i].addEventListener(event, funct);
}
}
}, 1000);
}
/**
* Now let's add live listener for "a" tags
*/
addLiveListener(document, "a.someBtn", "click", function() {
alert('Clicked ' + this.innerHTML);
});
a {
margin-right: 10px;
}
<!-- Add some pre-existing anchors -->
<p id="holder">
<a href="#" class="someBtn">Anchor 1</a><a href="#" class="someBtn">Anchor 2</a><a href="#" class="someBtn">Anchor 3</a>
</p>
<!-- A button to add dynamic new anchors -->
<input type="button" value="Add anchor" onclick="addAnchor();" />
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