How to trigger a javascript function on appearence of an element - javascript

Hi,
I need to execute a javascript function once as soon as an element with a given class appears on the code (the element will be generated by another script).
This is my function:
play(sound);
the element would appear inside this:
<div id="canvas">
The element would look like this:
<span class="sound">sound name</span>
where "sound name" will determine the argument for play();
how can this be done with javascript?
Thank you.

You can use a You could use a MutationObserver as shown below.
The second argument to .observe(), MutationObserverInit, is important:
In the options, use childList: true if the span will only be added as a direct child. subTree: true if it can be at any level down below #canvas.
From the docs:
childList: Set to true if additions and removals of the target node's child elements (including text nodes) are to be observed.
subtree: Set to true if mutations to target and target's descendants are to be observed.
$("#go").click(function () {
$("#canvas").append($('<span class="sound">sound name</span>'));
});
function play(n) { alert('playing '+ n); }
var obs = new MutationObserver(function(mutations, observer) {
$.each(mutations, function (i, mutation) {
var addedNodes = $(mutation.addedNodes);
var selector = "span.sound"
var spanSounds = addedNodes.find(selector).addBack(selector); // finds either added alone or as tree
spanSounds.each(function () { // handles any number of added spans
play($(this).text());
});
});
});
obs.observe($("#canvas")[0], {childList: true, subtree: true});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="canvas"></div>
<button id="go">Add span to canvas</button>
Using plain JavaScript
The code is a little less compact, but it is definitely doable:
document.getElementById("go").addEventListener('click', function () {
var s = document.createElement('span');
s.innerText = 'sound name';
s.classList.add('sound')
document.getElementById('canvas').appendChild(s);
});
function play(n) { alert('playing '+ n); }
var obs = new MutationObserver(function(mutations, observer) {
for(var i=0; i<mutations.length; ++i) {
for(var j=0; j<mutations[i].addedNodes.length; ++j) {
var addedNode = mutations[i].addedNodes[j];
//NOTE: if the element was added as child of another element, you would have to traverse
// the addedNode to find it. I recommend the jQuery solution above if that's the case
if(addedNode.tagName == "SPAN" && addedNode.classList.contains("sound")) {
play(addedNode.innerText);
}
}
}
});
obs.observe(document.getElementById('canvas'), {childList: true, subtree: true});
<div id="canvas"></div>
<button id="go">Add span to canvas</button>

You could probably try onload event

You need a listener to detect the DOM change, MutationObserver
// Select the node that will be observed for mutations
var targetNode = document.getElementById('some-id');
// Options for the observer (which mutations to observe)
var config = { attributes: true, childList: true };
// Callback function to execute when mutations are observed
var callback = function(mutationsList) {
for(var mutation of mutationsList) {
if (mutation.type == 'childList') {
console.log('A child node has been added or removed.');
}
else if (mutation.type == 'attributes') {
console.log('The ' + mutation.attributeName + ' attribute was modified.');
}
}
};
// Create an observer instance linked to the callback function
var observer = new MutationObserver(callback);
// Start observing the target node for configured mutations
observer.observe(targetNode, config);
// Later, you can stop observing
observer.disconnect();

Related

Is there an event listener to check if childElements have been added to an elements

I have a puppeteer project in which I'm waiting for some form of information on an Element. For example, in the header, I'm waiting for some new child Nodes.
<div id="outside">
</div>
and then after some time
<div id="outside">
<div id='inside'>
</div>
</div>
is there a way for me to add an event listener to check when the HTML has been changed?
something like
page.addListener('#outside', () => {
console.log('event fired');
}
You can try with MutationObserver
// Options for the observer (which mutations to observe)
const config = { attributes: true, childList: true, subtree: true };
// Callback function to execute when mutations are observed
const callback = function(mutationsList, observer) {
for(let mutation of mutationsList) {
if (mutation.type === 'childList') {
console.log('A child node has been added or removed.');
}
else if (mutation.type === 'attributes') {
console.log('The ' + mutation.attributeName + ' attribute was modified.');
}
}
};
// Create an observer instance linked to the callback function
const observer = new MutationObserver(callback);
const targetNode = document.querySelector('#outside');
// Start observing the target node for configured mutations
observer.observe(targetNode, config);
targetNode.insertAdjacentHTML('beforeend', "<div id='inside'>Child</div>"); // Add child
targetNode.classList.add('.child'); // Modify attribute
document.querySelector('#inside').style.marginLeft = '15px';
<div id="outside">Parent
</div>

MutationObserver to remove a div when style changes

I want to remove a div when the style changes. I have read that MutationObserver can do this. But the code that I tried is not working.
const observer = new MutationObserver(function
(mutations) {
mutations.forEach(function (mutation) {
if (mutation.attributes === 'style') {
removeDiv()
}
})
})
const elem = document.querySelector('.show-pl');
observer.observe(elem, {
attributes: true
})
function removeDiv() {
Object.assign(elem.style, {
display: 'none',
})
}
The addition of a new element has nothing to do with attributes, and you can't observe mutations on an element that isn't in the DOM yet.
Instead, you look for childList modifications on the parent element the div will be added within (or childList + subtree on an ancestor, if you can't watch the parent directly —if necessary, the ancestor can even be document.body).
Here's an example watching the parent directly:
// Set up the observer on the container
let observer = new MutationObserver(function() {
// Does the div exist now?
const div = document.querySelector(".show-pl");
if (div) {
// Yes, "remove" it (you're really just hiding it) and release this observer
console.log("The div has appeared, hiding and releasing observer");
div.style.display = "none";
observer.disconnect();
observer = null;
}
});
observer.observe(document.getElementById("the-parent"), {
childList: true
});
console.log("Watching for the element");
// On a delay, create the div
setTimeout(() => {
console.log("Creating the div");
const div = document.createElement("div");
div.textContent = "Hi there!";
div.className = "show-pl";
document.getElementById("the-parent").appendChild(div);
}, 800);
<div id="the-parent"></div>
To watch an ancestor instead you'd use the ancestor in the observe call and add subtree: true to the init options.
function removeDiv(canvas) {
var elem = document.querySelector('.show-pl');
elem.parentNode.removeChild(elem);
}
var observer = new MutationObserver(function (mutations, me) {
var canvas = document.querySelector(".show-pl");
if (canvas) {
removeDiv(canvas);
me.disconnect();
return;
}
});
observer.observe(document, {
childList: true,
subtree: true
});
This does what I want, but an error occurs "cannot read property 'addeventlistener' of null", because the div doesn't exists in the DOM yet.

How to listen to 'after' event?

I'm adding a new element dynamically via JQuery, with code like the below:
$('#example').after("<p class='xx'></p>")
Upon this code being called and a "xx" element being added, I'd like to run some other code. How can I 'listen' and pick up when this event happens?
Thanks
You can use Mutation Observer for this.
The demo below is a simple quick adaptation of the example in reference.
$(document).ready(function(){
var targetNode = document.getElementById('some-id');
var config = { attributes: true, childList: true, subtree: true };
var callback = function(mutationsList, observer) {
for(var mutation of mutationsList) {
if (mutation.type == 'childList') {
console.log('A child node has been added or removed.');
}
}
};
var observer = new MutationObserver(callback);
observer.observe(targetNode, config);
$('#example').after("<p class='xx'>I am a paragraph inserted by a script.</p>");
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="some-id">
<p id="example">I'm a static paragraph.</p>
</div>

How to keep track of DIV's child element count in runtime?

I have a div, which will contain dropdowns and these dropdowns are created dynamically by the user on the click oo a button which is kept outside this div.
So what I need to achieve here is I wanna display 'No filter applied' when there are no dropdowns and remove that 'No filter applied' while there are dropdowns present.
I tried this scenario through addEventListener but I am not sure what action needs to implement for this scenario?
document.addEventListener("DOMContentLoaded", function(event) {
var activities = document.getElementById("dvContainer");
activities.addEventListener("change", function() {
if (activities.childElementCount > 0) {
activities.classList.add("displayZero");
} else {
activities.classList.remove("displayZero");
}
//console.log('ajay');
});
});
function AddDropDownList() {}
<input type="button" id="btnAdd" onclick="AddDropDownList()" value="Add Filter" />
<div id="dvContainer"><span>No Filters applied.</span></div>
This is my try, thanks in advance.
According to what you mentioned, you have a button that with click it, you add dropdowns dynamically.
so you don't need any extra event!!
in your button's click function:
yourButton.onclick=function(){
//..... do somethings similar adding dropdowns
activities.classList.add("displayZero");
};
And where you remove dropdown:
activities.classList.remove("displayZero");
Currently, I can think of only 2 ways to resolve:
The Easiest solution is first to create update function then call it from init of dom and then in the AddDropDownList. E.g.
function update() {
if (activities.childElementCount > 0) {
activities.classList.add("displayZero");
} else {
activities.classList.remove("displayZero");
}
}
window.onload = function() {
update();
}
function AddDropDownList() {
//Put Your code as you have written and then add
update();
}
Use Mutation Observer
window.onload = function() {
// Select the node that will be observed for mutations
var targetNode = document.getElementById('dvContainer');
// Options for the observer (which mutations to observe)
var config = {
attributes: true,
childList: true,
subtree: true
};
// Create an observer instance linked to the callback function
var observer = new MutationObserver(callback);
// Start observing the target node for configured mutations
observer.observe(targetNode, config);
}
function AddDropDownList() {
}
// Callback function to execute when mutations are observed
var callback = function(mutationsList) {
for (var mutation of mutationsList) {
if (mutation.type == 'childList') {
console.log('A child node has been added or removed.');
if (activities.childElementCount > 0) {
activities.classList.add("displayZero");
} else {
activities.classList.remove("displayZero");
}
} else if (mutation.type == 'attributes') {
console.log('The ' + mutation.attributeName + ' attribute was modified.');
}
}
};

DOM Mutation Observer Callback and Child class for changed events

I have the following DOM Mutation Observer code:
<script type="text/javascript">
var targetNodes = $("#history");
var MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
var myObserver = new MutationObserver (mutationHandler);
var obsConfig = { childList: true, characterData: true, attributes: true, subtree: true };
//--- Add a target node to the observer. Can only add one node at a time.
targetNodes.each ( function () {
myObserver.observe (this, obsConfig);
} );
function mutationHandler (mutationRecords) {
console.info ("mutationHandler:");
mutationRecords.forEach ( function (mutation) {
$("span.badge").show();
} );
}
</script>
It is working fine when events changes are detected in #history id.
<p id="history"></p>
The problem is that i have some p.class inside #history as follows:
<p id="history">
<p class="mine"></p>
<p class="theirs"></p>
</p>
i need to detect the observer changes only in p class="theirs".
How is that possible only with child class, rather than observing DOM changes in #history id as a whole...
Introduction:
when you use the format:
$("#history").each ( function () {
myObserver.observe (this, obsConfig);
});
this is useless. $("#history") returns one element or nothing.
To test if a value is returned you may use
$("#history").length
This value in your case is 1. Remember that cannot exist more than one element with the same id (refer to: # selector).
In the each loop you use the this keyword. The value of this keyword is "Node target" element required from observe function.
So, because you have only one history element it's completely useless to cycle con only one element (refer: each function). Use the value by itself.
This value can be searched also with:
var target = document.getElementsByClassName('theirs')[0];
or
target = document.querySelectorAll('.theirs')[0];
or
target = $('.theirs').get(0);
Of course, if you do not have such new element on which to observe you cannot use the observe function.
For details see MutationObserver
The best way is to test the return value of the selected element, for instance:
if ($('.theirs').length == 0) {
// raise error and stop
} else {
target = $('.theirs').get(0);
}
Instead, if you have more than one element you may continue to use the each loop:
$(".theirs").each ( function () {
myObserver.observe (this, obsConfig);
});
My proposal:
According to HTML Paragraph tag you cannot have nested paragraphs.
If you need to observe only what happens for your 'theirs' paragraph you need simply to change a bit your code:
$(function () {
var targetNodes = $(".theirs");
var MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
var myObserver = new MutationObserver(mutationHandler);
var obsConfig = {childList: true, characterData: true, attributes: true, subtree: true};
// get the target node on which to observe DOM mutations
var target = document.getElementsByClassName('theirs')[0];
// another way to get the target is
target = document.querySelectorAll('.theirs')[0];
// another way to get the target is
if ($('.theirs').length == 0) {
// raise error and stop
} else {
target = $('.theirs').get(0);
}
myObserver.observe(target, obsConfig);
function mutationHandler(mutationRecords) {
alert("mutationHandler:");
mutationRecords.forEach(function (mutation) {
$("span.badge").show();
});
}
$('#btn').on('click', function (e) {
$('.theirs').text('Date Now is: ' + Date.now());
});
});
<script src="https://code.jquery.com/jquery-1.12.1.min.js"></script>
<div id="history">
<p class="mine"></p>
<p class="theirs"></p>
</div>
<button id="btn">Add text to theirs</button>
If you are interested in changes happening only for paragraphs added or changed inside the div with class theirs, according to the MutationRecord in the following I report only a demo on how to filter the events for new such added nodes (remember to start and stop the observer):
var myObserver = null;
function mutationHandler(mutationRecords, mutationInstance) {
// new node added
if (mutationRecords.length == 1 && mutationRecords[0].addedNodes.length == 1) {
// if element added is a paragraph with class theirs....
var eleAdded = $(mutationRecords[0].addedNodes[0]);
if (eleAdded.is('p.theirs')) {
alert("mutationHandler: added new paragraph with class theirs: " + eleAdded.text());
}
}
// if you need to listen for other events like attribute changed or element removed... please read the documentation regarding mutationRecords object
}
$(function () {
$('#startObserver').on('click', function(e) {
var targetNodes = $('#history');
var target = null;
if (targetNodes.length != 1) {
alert('Cannot start Observer on no element!')
return;
} else {
target = targetNodes.get(0);
}
var MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
myObserver = new MutationObserver(mutationHandler);
var obsConfig = {childList: true, characterData: true, attributes: true, subtree: true};
myObserver.observe(target, obsConfig);
});
$('#stopObserver').on('click', function(e) {
if (myObserver === null) {
alert('Cannot stop an Observer never started!')
} else {
myObserver.disconnect();
myObserver = null;
}
});
$('#btnMine').on('click', function (e) {
var txt = $('#mineInput').val();
$('#history').prepend('<p class="mine">Added mine paragraph with text: ' + (txt.trim() ? txt : 'empty text!') + '</p>');
});
$('#btnTheirs').on('click', function (e) {
var txt = $('#theirsInput').val();
$('#history').append($('<p class="theirs">Added theirs paragraph with text: ' + (txt.trim() ? txt : 'empty text!') + '</p>'));
});
});
<script src="https://code.jquery.com/jquery-1.12.1.min.js"></script>
<div id="history">
</div>
Mine paragraphs text: <input id="mineInput" type="text"><br>
Theirs paragraphs text: <input id="theirsInput" type="text"><br>
<button id="btnMine">Add new Mine paragrapgh</button>
<button id="btnTheirs">Add new Theirs paragrapgh</button><br><br>
<button id="startObserver">Start Observer</button>
<button id="stopObserver">Stop Observer</button>

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