I'm new to JavaScript. I know there are several posts on this topic, but I couldn't find one that seemed to quite address my problem.
I would like to change properties on elements with classes mainSlides and dot. But when I try to call those elements using getElementsByClassName, it returns undefined.
function showSlides(n) {
var i;
var slides = document.getElementsByClassName("mainSlides");
var dots = document.getElementsByClassName("dot");
if (n > slides.length) {slideIndex = 1}
if (n < 1) {slideIndex = slides.length}
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
for (i = 0; i < dots.length; i++) {
dots[i].className = dots[i].className.replace(" active", "");
}
slides[slideIndex-1].style.display = "block";
dots[slideIndex-1].className += " active";
When I inserted a breakpoint at var dots = document ... slides is undefined. Then I get an error at slides[slideIndex-1].style.display = "block";
Cannot read property 'style' of undefined
The HTML looks like this:
<div class="mainSlides fade">
<div class="numbertext">1 / 3</div>
<img src="images/mainSlide1.jpg" style="width:100%">
<div class="text">Caption Text</div>
</div>
and
<div style="text-align:center">
<span class="dot" onclick="currentSlide(1)"></span>
<span class="dot" onclick="currentSlide(2)"></span>
<span class="dot" onclick="currentSlide(3)"></span>
</div>
I'm not sure if my problem is in setting classes or using getElementsByClassName.
Your code has some logic problems:
If n > slides.length and n >= 1, then slideIndex = 1
If slides.length >= 1
OK, then you can use slides[slideIndex-1]
If slides.length === 0
Problem, slides[slideIndex-1] is undefined
If 1 <= n <= slides.length, then slideIndex is not set
slides[slideIndex-1] is probably a problem.
If n < 1, then slideIndex = slides.length
If slides.length >= 1
OK, then you can use slides[slideIndex-1]
If slides.length === 0
Problem, slides[slideIndex-1] is undefined
Related
why wouldn't this work? I am trying to make it so when you click on the video/div that the iframe video is in it would stop the automatic slider but I just can't get it to work.
javascript:
let slideIndex = 0;
showSlides();
let click = 0;
function clicked() {
var button = document.document.getElementsByClassName('slideshow-container');
button.addEventListener('slideshow-container', function handleClick() {
if (click = 1) {
click = 0;
}
else {
click = 1;
}
});
return click;
}
function showSlides() {
let i;
let slides = document.getElementsByClassName("slides");
let dots = document.getElementsByClassName("dot");
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
slideIndex++;
if (slideIndex > slides.length) {slideIndex = 1}
for (i = 0; i < dots.length; i++) {
dots[i].className = dots[i].className.replace(" active", "");
}
slides[slideIndex-1].style.display = "block";
dots[slideIndex-1].className += " active";
if (click != 1)
{
setTimeout(showSlides, 6666);
}
}
HTML:
<Center>
<div class="slideshow-container">
<div class="slides fade">
<div class="numbertext">1 / 3</div>
<iframe width="1000" height="500" src="https://www.youtube.com/embed/tgbNymZ7vqY"></iframe>
</div>
<div class="slides fade">
<div class="numbertext">2 / 3</div>
<iframe width="1000" height="500" src="https://www.youtube.com/embed/tgbNymZ7vqY"></iframe>
</div>
<div class="slides fade">
<div class="numbertext">3 / 3</div>
<iframe width="1000" height="500" src="https://www.youtube.com/embed/tgbNymZ7vqY"></iframe>
</div>
</div>
</br>
<div>
<span class="dot"></span>
<span class="dot"></span>
<span class="dot"></span>
</div>
</Center>
</div>
<br>
<script src="showSlides.js"></script>
Edit: as requested I swapped out the screenshots for the actual code and spent about 5 minutes trying to figure out how to actually post it and now I need more details but I don't know what to add so I'm writing this.
let slideIndex = 0;
var id = showSlides();
let click = 0;
function clicked() {
var button = document.document.getElementsByClassName('slideshow-container');
button.addEventListener('slideshow-container', function handleClick() {
if (click = 1) {
click = 0;
}
else {
click = 1;
}
});
return click;
}
function showSlides() {
let i;
let slides = document.getElementsByClassName("slides");
let dots = document.getElementsByClassName("dot");
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
slideIndex++;
if (slideIndex > slides.length) {slideIndex = 1}
for (i = 0; i < dots.length; i++) {
dots[i].className = dots[i].className.replace(" active", "");
}
slides[slideIndex-1].style.display = "block";
dots[slideIndex-1].className += " active";
if (click != 1)
{
var timeoutId = setTimeout(showSlides, 6666);
return timeoutId
}
}
Then to stop it, just call
clearTimeout(id)
My website has a simple slide carousel which works correctly, but the SEOptimer evaluation report says:
“Cannot read property 'className' of undefined at showSlides (http://www.abacus-arts.org.uk/:78:8) ”
Line 78 is near the end below and says: dots[slideIndex-1].className += " active";
Can I safely ignore the SEOptimer problem report, or can you help me to fix it?
<div>
<!-- code for slides 1 to 4 removed, below are slides 5 and 6 in the carousell -->
<div class="mySlides">
<div class="picnumber"> 5 / 6</div> <img src="Pic-5-DM.jpg" alt="Pic5" style="width:100%";>
<div class="pictitle"> Breakout room LHS view </div> </div>
<div class="mySlides">
<div class="picnumber"> 6 / 6</div> <img src="Pic-6-GW.jpg" alt="Pic6" style="width:100%";>
<div class="pictitle"> Street view of entrance </div> </div>
<!-- Back and forward buttons jump to the Java Script lower down -->
<a class="prev" onclick="plusSlides(-1)"> <</a>
<a class="next" onclick="plusSlides(1)"> ></a>
</div>
<!-- from https://www.w3schools.com/howto/howto_js_slideshow_gallery.asp -->
<script>
var slideIndex = 1;
showSlides(slideIndex);
function plusSlides(n) { showSlides(slideIndex += n); }
function currentSlide(n) { showSlides(slideIndex = n); }
function showSlides(n) { var i;
var slides = document.getElementsByClassName("mySlides");
// var dots = document.getElementsByClassName("demo");
// var captionText = document.getElementById("caption");
if (n > slides.length) {slideIndex = 1 }
if (n < 1) {slideIndex = slides.length }
for (i = 0; i < slides.length; i++) { slides[i].style.display = "none"; }
// for (i = 0; i < dots.length; i++)
// { dots[i].className = dots[i].className.replace(" active", ""); }
slides[slideIndex-1].style.display = "block";
// dots[slideIndex-1].className += " active";
// captionText.innerHTML = dots[slideIndex-1].alt;
}
</script>
UPDATE. Solved by removing the lines for unused variables as shown //.
#phuzi Thank you all for encouraging me to search for unused variables, I found in evolving the HTML I has stopped using "demo, dots and captiontext" and the problem went away when these code lines were excluded.
Many thanks. Graeme.
var dots = document.getElementsByClassName("demo");
there is null, it mean - i dont find any classes with name "demo"
check html part code
They actually have an inline javascript code and I am trying to convert it to an external javascript file. I want to get rid of my onclicks but I dont know how to rewrite my JS to be external. Here's the code I'm working at.
</div>
<a class="prev" onclick="plusSlides(-1)">❮</a>
<a class="next" onclick="plusSlides(1)">❯</a>
</div>
<br>
<div style="text-align:center">
<span class="dot" onclick="currentSlide(1)"></span>
<span class="dot" onclick="currentSlide(2)"></span>
<span class="dot" onclick="currentSlide(3)"></span>
<span class="dot" onclick="currentSlide(4)"></span>
</div>
<script>
let slideIndex = 1;
showSlides(slideIndex);
function plusSlides(n) {
showSlides(slideIndex += n);
}
function currentSlide(n) {
showSlides(slideIndex = n);
}
function showSlides(n) {
let i;
const slides = document.getElementsByClassName("mySlides");
const dots = document.getElementsByClassName("dot");
if (n > slides.length) {slideIndex = 1}
if (n < 1) {slideIndex = slides.length}
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
for (i = 0; i < dots.length; i++) {
dots[i].className = dots[i].className.replace(" active", "");
}
slides[slideIndex-1].style.display = "block";
dots[slideIndex-1].className += " active";
}
</script>
Simply, create js file. Like, script.js. Then, add your javascrript code inside the script.js. In script.js:
let slideIndex = 1;
showSlides(slideIndex);
function plusSlides(n) {
showSlides(slideIndex += n);
}
function currentSlide(n) {
showSlides(slideIndex = n);
}
function showSlides(n) {
let i;
const slides = document.getElementsByClassName("mySlides");
const dots = document.getElementsByClassName("dot");
if (n > slides.length) {slideIndex = 1}
if (n < 1) {slideIndex = slides.length}
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
for (i = 0; i < dots.length; i++) {
dots[i].className = dots[i].className.replace(" active", "");
}
slides[slideIndex-1].style.display = "block";
dots[slideIndex-1].className += " active";
}
Now, add the external file to the html file. Like:
<script src="script.js"></script>
You, can add this linking line in the head or at the bottom of body.
*Note:- If you add at the top i.e, head, then script will load first before the document inside body. Else, it will load after on.
I am working on a carousel in w3school. They actually have an inline javascript code and I am trying to convert it to an external javascript file. I have this code in my external file
window.addEventListener('DOMContentLoaded', function () {
var slideIndex = 1;
showSlides(slideIndex);
function currentSlide(n) {
showSlides(slideIndex = n);
}
function showSlides(n) {
var i;
var slides = document.getElementsByClassName("mySlides");
var dots = document.getElementsByClassName("dot");
if (n > slides.length) {slideIndex = 1}
if (n < 1) {slideIndex = slides.length}
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
for (i = 0; i < dots.length; i++) {
dots[i].className = dots[i].className.replace(" active", "");
}
slides[slideIndex-1].style.display = "block";
dots[slideIndex-1].className += " active";
}
}, false);
But when I navigate the carousel, it displays error Uncaught ReferenceError: currentSlide is not defined at HTMLSpanElement.onclick and does not work/navigate the images in the carousel
This is the HTML code
<div class="slideshow">
<div class="slideshow-container">
<div class="mySlides fade">
<img class="carousel-item" src="https://lorempixel.com/800/400/food/1">
</div>
<div class="mySlides fade">
<img class="carousel-item" src="https://lorempixel.com/800/400/food/2">
</div>
</div>
<div class="slide-nav">
<span class="dot" onclick="currentSlide(1)"></span>
<span class="dot" onclick="currentSlide(2)"></span>
</div>
</div>
<script type="text/javascript" src="js/components.js"></script>
Because currentSlide is not globally accessible (HTML inline event handlers run in the global scope). You need to define it in the global scope for it to work:
function currentSlide(n) {
showSlides(slideIndex = n);
}
window.addEventListener("DOMContentLoaded", function() {...}, false);
So I'm trying to learn JavaScript but in the mean time I'm manipulating other's code, such as w3school's. I thought I could manage this but am struggling.
I'm trying to remove anything to do with the dot, numbering and caption from this script. I can work through process of elimination but I'd rather not end up with some messy script.
This is a link to the complete code https://www.w3schools.com/howto/tryit.asp?filename=tryhow_js_slideshow_auto
Thank you in advance..
<script>
var slideIndex = 0;
showSlides();
function showSlides() {
var i;
var slides = document.getElementsByClassName("mySlides");
var dots = document.getElementsByClassName("dot");
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
slideIndex++;
if (slideIndex> slides.length) {slideIndex = 1}
for (i = 0; i < dots.length; i++) {
}
slides[slideIndex-1].style.display = "block";
setTimeout(showSlides, 4000); // Change image every 2 seconds
}
</script>
Its not that hard :)
Here you have it:
<div class="slideshow-container">
<div class="mySlides fade">
<img src="img_nature_wide.jpg" style="width:100%">
</div>
<div class="mySlides fade">
<img src="img_fjords_wide.jpg" style="width:100%">
</div>
<div class="mySlides fade">
<img src="img_mountains_wide.jpg" style="width:100%">
</div>
</div>
<br>
<script>
var slideIndex = 0;
showSlides();
function showSlides() {
var i;
var slides = document.getElementsByClassName("mySlides");
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
slideIndex++;
if (slideIndex> slides.length) {slideIndex = 1}
slides[slideIndex-1].style.display = "block";
setTimeout(showSlides, 2000); // Change image every 2 seconds
}
</script>
Furthermore you might want to remove the unnecesary css classes.