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JavaScript last element of HTML collection not defined

I am trying to create a bookable product, where upon selected (= selectbox) a room type, the picture changes to that specific room with good old javascript.
the interesting part is that it works for the first element of the HTML collection, but the last element is giving an undefined and makes it impossible to override.
I am not getting why that is. I tried via the console log to view what I am missing, but I see nothing problematic.
HTML collection:
0: <a href="https://staging.deloftli…09/Steck-coachruimte.jpg" hidefocus="true" style="outline: currentcolor none medium;">​
1: <img class="zoomImg" role="presentation" alt="" src="https://staging.deloftli…09/Steck-coachruimte.jpg" style="position: absolute; top:…none; max-height: none;">
I have the following script:
<script id="bookingschanges">
var activities = document.getElementById("wc_bookings_field_resource");
var image = document.getElementsByClassName("woocommerce-product-gallery__image")[0].children[0].firstChild;
var zoompic = document.getElementsByClassName("woocommerce-product-gallery__image")[0].children[1];
activities.addEventListener("click", function() {
var options = activities.querySelectorAll("option");
});
activities.addEventListener("change", function() {
if(activities.value == "1949")
{
image.src = "https://staging.deloftlisse.nl/wp-content/uploads/2021/09/Podkas.jpeg";
image.srcset = ""
zoompic.scr = "https://staging.deloftlisse.nl/wp-content/uploads/2021/09/Podkas.jpeg";
}
console.log(image);
console.log(zoompic);
});</script>
The first element (image) is correct, the second element (zoompic) gives undefined.
To see it live, go to https://staging.deloftlisse.nl/product/vergaderruimte-huren/ and check the console log.
What am I missing here?

Variable zoompic is not defined at the time the variable is declared (its called before the element is created on loading, debug the page and refresh it to see) you will need to use an onload event listener.
https://developer.mozilla.org/en-US/docs/Web/API/Window/load_event
As someone else has suggested it would be better to call the image change function in the original javascript to change the image that is selected and you will avoid any issues. This might not be easy though if it is an external library.
EDIT: Added an example of onLoad
window.addEventListener('load', (event) => {
var activities = document.getElementById("wc_bookings_field_resource");
var image = document.getElementsByClassName("woocommerce-product-gallery__image")[0].children[0].firstChild;
var zoompic = document.getElementsByClassName("woocommerce-product-gallery__image")[0].children[1];
activities.addEventListener("click", function() {
var options = activities.querySelectorAll("option");
});
activities.addEventListener("change", function() {
if (activities.value == "1949") {
image.src = "https://staging.deloftlisse.nl/wp-content/uploads/2021/09/Podkas.jpeg";
image.srcset = "https://staging.deloftlisse.nl/wp-content/uploads/2021/09/Podkas.jpeg 768w";
zoompic.src = "https://staging.deloftlisse.nl/wp-content/uploads/2021/09/Podkas.jpeg";
}
console.log(image);
console.log(zoompic);
})
});

Assign array of image elements to DOM ids

I have an array of URIs that represent .png elements, e.g., "./img/diamond-red-solid-1.png".
I want to assign each element of the array "gameDeck[0], gameDeck[1], etc. to div ids in HTML. Do I need to identify the elements as = SRC.IMG?
var gameDeck[];
var gameBoardCards = function () {
for (let cardArr of cardsToLoad)
gameDeck.push("./img/" + cardArr + ".png");
}
gameBoardCards();
document.addEventListener('DOM Content Loaded', function () {
gameDeck[0] = document.getElementById("card1");
gameDeck[1] = document.getElementById("card2");
etc.
});

The way I'm understanding your question is that you would like to target the divs in your HTML with ids of card1, card2, card3... card12 etc.
You would like to insert an img tag into each of these divs with the src being the URIs of the gameDeck array.
The following code achieves this. I've tested it and it works fine. Hope it helps :)
document.addEventListener('DOMContentLoaded', function () {
//iterate through the gameDeck array.
for (let x = 0;x < gameDeck.length;x++){
//create an img tag for each gameDeck element
var imgElement = document.createElement("img");
//set the source of the img tag to be the current gameDeck element (which will be a URI of a png file)
imgElement.src = gameDeck[x];
//target the div with id "card(x + 1)"
var cardID = "card" + (x + 1);
var cardElement = document.getElementById(cardID);
//append the img tag to the card element
cardElement.appendChild(imgElement);
}
//log the HTML to the console to check it
console.log(document.getElementById('body').innerHTML);
});

Here is a way that you can either insert images as background images, or as <img /> elements into the divs you are referring to:
<div id="card0" style="width: 100px; height: 100px;"></div>
<div id="card1" style="width: 100px; height: 100px;"></div>
let loadedImage = [];
function preloadImages(urls, allImagesLoadedCallback) {
let loadedCounter = 0;
let toBeLoadedNumber = urls.length;
urls.forEach(function(url) {
preloadImage(url, function() {
loadedCounter++;
console.log(`Number of loaded images: ${loadedCounter}`);
if (loadedCounter == toBeLoadedNumber) {
allImagesLoadedCallback();
}
});
});
function preloadImage(url, anImageLoadedCallback) {
img = new Image();
img.src = url;
img.onload = anImageLoadedCallback;
loadedImage.push(img);
}
}
function gameBoardCards() {
for (let i = 0; i < loadedImage.length; i++) {
document.getElementById(`card${i}`).style.backgroundImage = `url('${loadedImage[i].src}')`;
// document.getElementById(`card${i}`).appendChild(loadedImage[i]);
}
}
preloadImages([
`https://upload.wikimedia.org/wikipedia/commons/thumb/7/7d/Color_icon_green.svg/2000px-Color_icon_green.svg.png`, `https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Solid_blue.svg/225px-Solid_blue.svg.png`
], function() {
console.log(`all images were loaded`);
gameBoardCards();
// continue your code
});
It may seem like a bit much for what you are trying to accomplish, but I threw in a proper image-loading handler there. The preloadImages function will handle the loading of images, that way they are properly preloaded, and can render to the DOM. Often times, we try to use images before they are properly loaded, resulting in them sometimes not being displayed, despite no errors are being thrown.
The rest of the code is straight forward, in the for loop, it loops through the existing divs and you can either use the current active line document.getElementById(`card${i}`).style.backgroundImage = `url('${loadedImage[i].src}')`; to use the loadedImage[i] image src to load that as the divs's background image. Or you can use the commented-out line directly below that document.getElementById(`card${i}`).appendChild(loadedImage[i]); to insert an <img /> element into that div. Just use either one that works for you.
You can see the code in action in this JS Fiddle demo.
Hope this helps :)

Change Image Source from Div with onmouseover

Is it possible to change the image source from the containing div? The images are dynamic and pulled from the database.
v = $"<div onmouseover=\"document.navIcon.src='/Images/White/{reader[2]}';\"
onmouseout=\"document.navIcon.src='/Images/{reader[2]}';\">
<img name=\"navIcon\" src=\"Images/{reader[2]}\"><br>{reader[1]}</div>";
That was my thoughts on how to do it but it doesn't appear to work as expected. I was able to get it to work when I put the onmouseover portion in the < img > however, I want it to change anywhere in the div, like over the reader[1] text, not just directly over the image.
Thoughts?

I just grabbed some images off google images. You can use this to refer to the current element.
<img
src='https://osu.ppy.sh/forum/images/smilies/50.gif'
onmouseover='this.src="http://4.bp.blogspot.com/-YrmTHhfMtFU/VJNbpDMHzgI/AAAAAAAAH8c/g3dJ1Q-QTrc/s1600/smile.png"'
onmouseout='this.src="https://osu.ppy.sh/forum/images/smilies/50.gif"'
/>
Edit..
This will change the image when you hover on anything with a "hoverme" class name.
(function() {
var img1 = "https://osu.ppy.sh/forum/images/smilies/50.gif";
var img2 = "http://4.bp.blogspot.com/-YrmTHhfMtFU/VJNbpDMHzgI/AAAAAAAAH8c/g3dJ1Q-QTrc/s1600/smile.png";
var myimg = document.getElementById('myimg');
myimg.src = img1;
var hoverables = document.getElementsByClassName('hoverme');
for (var i = hoverables.length; i--;) {
hoverables[i].addEventListener("mouseover", hoverMe, false);
hoverables[i].addEventListener("mouseout", unhoverMe, false);
}
function hoverMe() {
myimg.src = img2;
}
function unhoverMe() {
myimg.src = img1;
}
})();
<img class='hoverme' id='myimg' />
<p class='hoverme'>poooooooop</p>
<div class='hoverme'>This si a diiiiivvvvv</div>

The best way to accomplish that is to use CSS.
HTML
<img id="NavIcon">
CSS
#Navicon {
background-image: url(image1.jpg);
}
#NavIcon:hover {
background-image: url(image2.jpg);
}

How can I check if the href path contain image or someother link using javascript or jquery?

Any One Know Tell me the suggestion to do this. How can i check if the anchor href attribute contain image path or some other path.
For Example:
<img src="image.jpg"/>
<img src="image.jpg"/>
See the above example shows href attribute contain different path like first one is the image and second one is the some other site link. I still confuse with that how can i check if the href path contain the image path or some other path using jquery or javascript.
Any suggestion would be great.

For example (you may need to include other pic formats if needed):
$("a").each(function(i, el) {
var href_value = el.href;
if (/\.(jpg|png|gif)$/.test(href_value)) {
console.log(href_value + " is a pic");
} else {
console.log(href_value + " is not a pic");
}
});

Jquery:
$(document).ready( function() {
var checkhref = $('a').attr('href');
var image_check = checkhref.substr(checkhref.length - 4)
http_tag = "http";
image = [".png",".jpg",".bmp"]
if(checkhref.search("http_tag") >= 0){
alert('Http!');
//Do something
}
if($.inArray(image_check, image) > -1){
alert('Image!');
//Do something
}
});

you may check if image exists or not, without jQuery
Fiddle
var imagesrc = 'http://domain.com/image.jpg';
function checkImage(src) {
var img = new Image();
img.onload = function() {
document.getElementById("iddiv").innerHTML = src +" exists";
};
img.onerror = function() {
document.getElementById("iddiv").innerHTML = src +"does not exists";
};
img.src = src; // fires off loading of image
return src;
}
checkImage(imagesrc);

append string to image src using js

I've got a page where there is <img src="/images/product/whatever-image.jpg" alt="" />
I want it so that upon loading of the page, the string "?Action=thumbnail" is appended to src's value, making it src="/images/product/whatever-image.jpg?Action=thumbnail"
how do I achieve this using js?

window.addEventListener('load', function(){
/* assuming only one img element */
var image = document.getElementsByTagName('img')[0];
image.src += '?Action=thumbnail';
}, false);
Note, changing the source of the image will "re-fetch" the image from the server — even if the image is the same. This will be better done on the server-side.
Update after comment:
window.addEventListener('load', function(){
/* assuming only one div with class "divclassname" and img is first child */
var image = document.getElementsByClassName('divclassname')[0].firstChild;
image.src += '?Action=thumbnail';
}, false);

Use this:
window.onload = function() {
document.getElementById('myImage').src += "/Action=thumbnail";
};