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How toggle elements inside this intersection observer?

I have a few elements I want to toggle wth a function, but by some reason I can't make it work. When the toggle function is executed, the console logs "cannot read the property classList of Undefined". But if I log them before the function starts I can see the elements.
Javascript
const toggle = element => {
element.classList.toggle('toggle');
};
let numberOfProyects = document.getElementsByClassName('portfolio__item'),
proyects = [],
for (var i = 0; i < numberOfProyects.length; i++) {
proyects[i] = document.getElementById(`proyect${i+1}`);
console.log(proyects[i]);
new IntersectionObserver(()=>{
toggle(proyects[i])
},{threshold: .6}).observe(proyects[i]);
};
HTML
<div class="portfolio__item toggle" id="proyect1">
<h3 class="portfolio__item-title">Podomoro Timer</h3>
<img class="portfolio__item-img" src="assets/images/Captura de pantalla (316).png">
<div class="portfolio__item-links">
<div class="overlay portfolio__item-links-overlay">
<a target="_blank" href="https://js-codetalker.github.io/Timer/" class="portfolio__item-links-overlay-link">
<img src="assets/images/world.svg" class="portfolio__item-links-overlay-link-img">
<p class="portfolio__item-links-overlay-link-txt">Go proyect</p>
</a>
</div>
<div class="overlay portfolio__item-links-overlay">
<a target="_blank" href="https://github.com/Js-codetalker/Timer" class="portfolio__item-links-overlay-link">
<img src="assets/images/github.svg" class="portfolio__item-links-overlay-link-img">
<p class="portfolio__item-links-overlay-link-txt">Go github</p>
</a>
</div>
</div>
</div>
<div class="portfolio__item toggle" id="proyect2">
<h3 class="portfolio__item-title">Sample Restaurant</h3>
<img class="portfolio__item-img" src="assets/images/Captura de pantalla (317).png">
<div class="portfolio__item-links">
<div class="overlay portfolio__item-links-overlay">
<a target="_blank" href="https://js-codetalker.github.io/restaurant-example/" class="portfolio__item-links-overlay-link">
<img src="assets/images/world.svg" class="portfolio__item-links-overlay-link-img">
<p class="portfolio__item-links-overlay-link-txt">Go proyect</p>
</a>
</div>
<div class="overlay portfolio__item-links-overlay">
<a target="_blank" href="https://github.com/Js-codetalker/restaurant-example" class="portfolio__item-links-overlay-link">
<img src="assets/images/github.svg" class="portfolio__item-links-overlay-link-img">
<p class="portfolio__item-links-overlay-link-txt">Go github</p>
</a>
</div>
</div>
</div>
What I want is to create a different observer for each element in order to remove the class "toggle" when it reach the expected space in the viewport

(almost) Always use let instead of var when defining variables inside for loops
Also, you don't need store your elements in second array.
const toggle = element => {
element.classList.toggle('toggle');
console.log(element);
};
const proyects = document.getElementsByClassName('portfolio__item');
for (let i = 0; i < proyects.length; i++) {
new IntersectionObserver(() => {
toggle(proyects[i])
}, {
threshold: .6
}).observe(proyects[i]);
};
.container
{
border: 1px solid black;
resize: both;
overflow: auto;
width: 20em;
height: 10em;
}
.container > :after
{
content: attr(id) " class is " attr(class);
}
.container > :not(.toggle) {
background-color: pink;
}
.container >.toggle {
background-color: lightgreen;
}
<div class="container">
<div class="portfolio__item toggle" id="proyect1">
<h3 class="portfolio__item-title">Podomoro Timer</h3>
</div>
<div class="portfolio__item" id="proyect2">
<h3 class="portfolio__item-title">Sample Restaurant (has not toggle by default)</h3>
</div>
<div class="portfolio__item toggle" id="proyect3">
<h3 class="portfolio__item-title">test</h3>
</div>
<div class="portfolio__item toggle" id="proyect4">
<h3 class="portfolio__item-title">test</h3>
</div>
</div>

play pause button to toggle button

please help me, play/pause button to one toggle button
mean one time click audio is play second time click then audio is pause with icon change. thanks in advance
.d-table {
display:table !important;
}
.d-table-cell {
display:table-cell !important;
}
.w-100 {
width: 100% !important;
}
.tar {
text-align: left !important;
}
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
<div class=" d-table w-100">
<p class="d-table-cell">بِسْمِ ٱللَّهِ ٱلرَّحْمَٰنِ ٱلرَّحِيمِ</p>
<div class="d-table-cell tar w-10">
<audio id="player2" src="http://www.mp3naat.com/download/owais-raza-qadri/mustafa-jaan-e-rehmat.mp3"></audio>
<a onclick="document.getElementById('player2').play()"><i class="fa fa-play-circle-o fa-2x"></i></a>
<a onclick="document.getElementById('player2').pause()"><i class="fa fa-pause-circle-o fa-2x"></i></a>
</div>
</div>

Try this. It will toggle as well as play and pause on click
var play = false;
var audio=document.getElementById('player2');
function toggle() {
if (play) {
audio.pause()
} else {
audio.play();
}
};
audio.onplaying = function() {
play = true;
};
audio.onpause = function() {
play = false;
};
$(".w-10 >a> #a").click(function(){$(this).toggleClass("fa-play-circle-o fa-pause-circle-o")})
.d-table {
display:table !important;
}
.d-table-cell {
display:table-cell !important;
}
.w-100 {
width: 100% !important;
}
.tar {
text-align: left !important;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
<div class=" d-table w-100">
<p class="d-table-cell">بِسْمِ ٱللَّهِ ٱلرَّحْمَٰنِ ٱلرَّحِيمِ</p>
<div class="d-table-cell tar w-10">
<audio id="player2" src="http://www.mp3naat.com/download/owais-raza-qadri/mustafa-jaan-e-rehmat.mp3"></audio>
<a onclick="toggle()"><i id="a" class="fa fa-play-circle-o fa-2x"></i></a>
</div>
</div>

change your html like this
<div class=" d-table w-100">
<p class="d-table-cell">بِسْمِ ٱللَّهِ ٱلرَّحْمَٰنِ ٱلرَّحِيمِ</p>
<div class="d-table-cell tar w-10">
<audio id="player2" src="http://www.mp3naat.com/download/owais-raza-qadri/mustafa-jaan-e-rehmat.mp3"></audio>
<a id="toggle-button"><i id="icons" class="fa fa-play-circle-o fa-2x"></i></a>
</div>
</div>
and javascript
<script>
var count =0;
document.getElementById("toggle-button").onclick = function() {
console.log("hello");
if(count%2==0){
document.getElementById("player2").play();
document.getElementById("icons").classList.remove("fa-play-circle-o");
document.getElementById("icons").classList.add("fa-pause-circle-o");
}else{
document.getElementById("player2").pause();
document.getElementById("icons").classList.add("fa-play-circle-o");
document.getElementById("icons").classList.remove("fa-pause-circle-o");
}
count++;
}
</script>

Check if a element is visible

I want to check if an element is visible and play a song only when it is, using: a trigger('click') event handler.
Unfortunately, I can't get it working as expected.
What am I doing wrong and how can I fix it?
Here is my JavaScript code (jQuery):
$('.overlay').on('click', function () {
if ($('a.icon-play').is(':hidden') == false) {
$('#stop').trigger('click');
} else {
$('#play').trigger('click');
}
});
Below is my HTML code:
<div class="info">
<div class="player-home-video">
<audio id="yourownlullaby-audio" src="uploads/downloads/Buenas%20%20Noches%20%3C?php%20echo%20$_POST['name'];%20?%3E.mp3"></audio>
</div>
<div class="thumbnail-home-video">
<a href="#" id="play">
<span class="icon-play preview-icon" id="play"></span>
</a>
<a href="#" id="stop">
<span class="icon-pause preview-icon" id="stop"></span>
</a>
<img class="info" src="img/thumbnail-home-video.png" />
<div class="overlay"></div>
</div>
</div>

$('.overlay').on('click', function () {
if ($('a .icon-play').is(':hidden') == true) {
$('#stop').trigger('click');
}
else
{
$('#play').trigger('click');
} });
Your​ if should be the other way.

Javascript doesn't toggle the display of an element

So, I'm trying to obtain multiple slideshows on my website.
I have done almost everything, excepting the fact that when I press a picture, the modal of previews is showing, but the clicked image is not showing up. I have to use the buttons of the slideshow to go through them and make the first one to appear.
**
If you don't want to go along this whole code, here you can see what's happening: http://beta.eduardstefan.com
**
I am not trying to promote myself, I just think that I am not quite easy to understand without the example
So, my question, how can I make the first picture to show up when I press one, or why it's not happening, what is bad with my code?
My html:
<div class="portfolio-slideshow">
<a class="prev" onclick="slide(0,-1)">❮</a>
<div class="slide"> <img src="img/dailyui/008.png" class="slideimg_0" id="0" data-no="0"> </div>
<div class="slide"> <img src="img/dailyui/007.jpg" class="slideimg_0" id="1" data-no="0"> </div>
<div class="slide"> <img src="img/dailyui/006.jpg" class="slideimg_0" id="2" data-no="0"> </div>
<div class="slide"> <img src="img/dailyui/003.jpg" class="slideimg_0" id="3" data-no="0"> </div>
<a class="next" onclick="slide(0,1)">❯</a>
</div>
<div class="portfolio-slideshow">
<a class="prev" onclick="slide(2,-1)">❮</a>
<div class="slide"> <img src="img/dailyui/008.png" class="slideimg_2" id="0" data-no="2"> </div>
<div class="slide"> <img src="img/dailyui/007.jpg" class="slideimg_2" id="1" data-no="2"> </div>
<div class="slide"> <img src="img/dailyui/006.jpg" class="slideimg_2" id="2" data-no="2"> </div>
<div class="slide"> <img src="img/dailyui/003.jpg" class="slideimg_2" id="3" data-no="2"> </div>
<a class="next" onclick="slide(2,1)">❯</a>
</div>
<div class="imgpreview">
<i class="fa fa-close" onclick="closepreview()"></i>
<div class="slidepreview no_0">
<a class="prev" onclick="slide(1,-1)">❮</a>
<div class="slidep"> <img src="img/dailyui/008.png" class="slideimg_1" id="0"> </div>
<div class="slidep"> <img src="img/dailyui/007.jpg" class="slideimg_1" id="1"> </div>
<div class="slidep"> <img src="img/dailyui/006.jpg" class="slideimg_1" id="2"> </div>
<div class="slidep"> <img src="img/dailyui/003.jpg" class="slideimg_1" id="3"> </div>
<a class="next" onclick="slide(1,1)">❯</a>
</div>
<div class="slidepreview no_2">
<a class="prev" onclick="slide(3,-1)">❮</a>
<div class="slidep"> <img src="img/dailyui/008.png" class="slideimg_3" id="0"> </div>
<div class="slidep"> <img src="img/dailyui/007.jpg" class="slideimg_3" id="1"> </div>
<div class="slidep"> <img src="img/dailyui/006.jpg" class="slideimg_3" id="2"> </div>
<div class="slidep"> <img src="img/dailyui/003.jpg" class="slideimg_3" id="3"> </div>
<a class="next" onclick="slide(3,1)">❯</a>
</div>
</div>
SCSS:
.portfolio-slideshow{
width: 30%;
display: flex;
justify-content: space-between;
align-items: center;
}
.slide{
padding:0 35px;
display: block;
img{
display: none;
max-height:40vh;
max-width:100%;
}
}
.prev,.next{
display: flex;
align-items: center;
justify-content: center;
}
.imgpreview{
display: none;
position: fixed;
top: 0;
left: 0;
width: 100vw;
height: 100vh;
background: rgba(0,0,0,0.9);
justify-content: center;
align-items: center;
padding: 50px;
}
.slidepreview{
display: none;
align-items: center;
justify-content: center;
.slidep{
display: block;
img{
display: none;
max-height: 85vh;
max-width: 85vw;
}
}
And Javascript:
var slideIndex = [0,0,0,0,0,0,0,0]
function showSlides(){
var aux = slideIndex.length;
var i;
for(i=0; i<aux; i+=2) { slide(i,0); }
}
function slide(n,m){
var i;
var aux = document.getElementsByClassName("slideimg_" + n);
var aux2 = aux.length - 1;
if (slideIndex[n] == 3 && m == 1) slideIndex[n] = -1;
if (slideIndex[n] == 0 && m == -1) slideIndex[n] = 4;
slideIndex[n] += m;
if (slideIndex[n] < 0) slideIndex = aux2;
else if (slideIndex[n] > aux2) slideIndex = 0;
for(i=0; i<aux.length; i++){
aux[i].style.display = "none";
aux[i].parentElement.style.display = 'none';
}
aux[slideIndex[n]].style.display = "block";
aux[slideIndex[n]].parentElement.style.display = 'block';
}
function closepreview(){
$('.imgpreview').css("display" , "none");
$('.slidepreview').css("display" , "none")
}
$(document).ready(function() {
$(".slide img").click(function(){
var id = $(this).attr('id');
var no = $(this).attr('data-no');
var no2 = no + 1;
$(".imgpreview").css("display" , "flex");
$(".no_" + no).css("display" , "flex");
$("img#" + id + ".slideimg_" + no2).css("display" , "block");
slideIndex[no2] = id;
});
}).resize();

The IDs must be unique.
Instead of inline event handlers I would suggest to attach them to the js code (separate html from js code).
I removed all IDs and I changed everything in jQuery using:
.index()
.toggle( display )
.nextAll(), .next(), .prev() and .prevAll()
I used a class: active. This class is used to mark the current active element. Moreover, every time I need to move next or prev I move this class to the corresponding element. This class takes track of which img must be shown.
The snippet:
$(document).ready(function() {
//
// Toggle visibility
//
$('.slide:not(.active), .slide:not(.active) img').toggle(false);
$('.slide.active, .slide.active img').toggle(true);
//
// closing preview....
//
$('.imgpreview .fa.fa-close').on('click', function(e) {
$('.imgpreview, .slidepreview').css("display" , "none");
//
// ...remove active class and toggle visibility
//
$('.imgpreview, .slidepreview').find('.active, .active img').toggleClass(false).removeClass('active');
});
//
// on prev....
//
$(".prev").on('click', function(e) {
//
// get the active element and so the previous one
//
var active = $(this).nextAll('.slide.active');
var prev = active.prev('.slide');
if (prev.length == 0) {
//
// if at the beginning take the last one
//
prev = $(this).nextAll('.slide').last();
}
//
// move active class and toggle visibility
//
active.removeClass('active');
prev.addClass('active').find('img').andSelf().toggle(true);
$('.slide:not(.active), .slide:not(.active) img').toggle(false);
});
$(".next").on('click', function(e) {
//
// get the active element and so the next one
//
var active = $(this).prevAll('.slide.active');
var next = active.next('.slide');
if (next.length == 0) {
//
// if at the end take the first one
//
next = $(this).prevAll('.slide').last();
}
//
// move active class and toggle visibility
//
active.removeClass('active');
next.addClass('active').find('img').andSelf().toggle(true);
$('.slide:not(.active), .slide:not(.active) img').toggle(false);
});
$(".slide img").on('click', function(e) {
//
// take the index of curr element in the parent element
//
var idx = $(this).closest('div.slide').index();
var no = $(this).data('no');
$('.imgpreview, .no_' + no).css('display' , 'flex');
$('.no_' + no).children().eq(idx).addClass('active');
$('.no_' + no).find('.slide:not(.active), .slide:not(.active) img').toggle(false);
$('.no_' + no).find('.slide.active, .slide.active img').toggle(true);
});
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link rel="stylesheet" href="http://beta.eduardstefan.com/css/style.css">
<link rel="stylesheet" href="http://beta.eduardstefan.com/css/font-awesome.css">
<div class="portfolio-slideshow">
<a class="prev">❮</a>
<div class="slide active"> <img src="http://beta.eduardstefan.com/img/dailyui/008.png" class="slideimg_0" data-no="0"></div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/007.jpg" class="slideimg_0" data-no="0"></div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/006.jpg" class="slideimg_0" data-no="0"></div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/003.jpg" class="slideimg_0" data-no="0"></div>
<a class="next">❯</a>
</div>
<div class="portfolio-slideshow">
<a class="prev">❮</a>
<div class="slide active"> <img src="http://beta.eduardstefan.com/img/dailyui/008.png" class="slideimg_2" data-no="2"></div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/007.jpg" class="slideimg_2" data-no="2"></div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/006.jpg" class="slideimg_2" data-no="2"> </div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/003.jpg" class="slideimg_2" data-no="2"></div>
<a class="next">❯</a>
</div>
<div class="imgpreview">
<i class="fa fa-close"></i>
<div class="slidepreview no_0">
<a class="prev" onclick="slide(1,-1)">❮</a>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/008.png" class="slideimg_1"></div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/007.jpg" class="slideimg_1"></div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/006.jpg" class="slideimg_1"></div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/003.jpg" class="slideimg_1"></div>
<a class="next">❯</a>
</div>
<div class="slidepreview no_2">
<a class="prev">❮</a>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/008.png" class="slideimg_3"></div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/007.jpg" class="slideimg_3"></div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/006.jpg" class="slideimg_3"></div>
<div class="slide"> <img src="http://beta.eduardstefan.com/img/dailyui/003.jpg" class="slideimg_3"></div>
<a class="next">❯</a>
</div>
</div>

At least one problem is here:
var no = $(this).attr('data-no');
var no2 = no + 1;
no is a string so if no is "0", then no + 1 is "01", so instead you can do this:
var no = $(this).attr('data-no');
var no2 = Number(no) + 1;
https://codepen.io/anon/pen/MmwdZb?editors=1111
Beyond that, why re-invent the wheel? There are plenty of good slideshow plugins available.

How can I hide one div before opening another?

How can I make it so that only one div can be shown at a time? I've tried adding "document.getElementById(currentID).style.display='none';" in the after the else but that doesn't work.
<h5 onclick="showImage('chair')">Chair</h5>
<h5 onclick="showImage('table')">Table</h5>
<h5 onclick="showImage('long_table')">Meeting Table</h5>
<div id="chair">
<img src="images/1.jpg" height="300px"/>
<h4>Product 1</h4>
</div>
<div id="table">
<img src="images/2.jpg" height="300px"/>
<h4>Product 2</h4>
</div>
<div id="longtable">
<img src="images/3.jpg" height="300px"/>
<h4>Product 3</h4>
</div>
<script type="text/javascript">
var currentID = "";
function showImage(id){
if(currentID == id){
document.getElementById(id).style.display='none';
currentID = "";
}else{
document.getElementById(id).style.display='block';
currentID = id;
}
}
</script>

Better to add a class to your HTML and then grab the divs by their class. You can then loop through the elements to hide them all and then un-hide the one you've clicked.
Example:
var arrProducts = document.getElementsByClassName('product');
for (i = 0; i < arrProducts.length; i++) {
arrProducts[i].style.display = 'none';
}
function showImage(id) {
for (i = 0; i < arrProducts.length; i++) {
if (id == arrProducts[i].id) {
if (document.getElementById(id).style.display === 'none') {
arrProducts[i].style.display = 'block';
} else {
arrProducts[i].style.display = 'none';
}
} else {
arrProducts[i].style.display = 'none';
}
}
}
h5 {
cursor: pointer;
}
.product img {
height: 10px;
width: 10px;
}
<h5 onclick="showImage('chair');">Chair</h5>
<h5 onclick="showImage('table');">Table</h5>
<h5 onclick="showImage('long_table');">Meeting Table</h5>
<div class="product" id="chair">
<img src="images/1.jpg" height="300px" />
<h4>Product 1 (Chair)</h4>
</div>
<div class="product" id="table">
<img src="images/2.jpg" height="300px" />
<h4>Product 2 (Table)</h4>
</div>
<div class="product" id="long_table">
<img src="images/3.jpg" height="300px" />
<h4>Product 3 (Meeting Table)</h4>
</div>

While this won't help you fix things in you current code, you can actually do this without any JavaScript by abusing radiobuttons. This is quite common.
http://jsfiddle.net/mo7yppp8/
Each div needs a radio button above it, and to be enclosed within a label. This way, clicking on the div will trigger the radiobutton, deselecting any other div in the process.
<label>
<input class="divSelector" type="radio" name="divSelector" value="" />
<div>Sample text</div>
</label>
Then, all you need is some CSS to hide the radiobuttons, and some to shrink the divs which aren't right after a checked input.
.divSelector {
display: none;
}
.divSelector:checked + div {
font-size: 12pt;
}
div {
font-size: 0pt;
background-color: blue;
color: white;
overflow: clip;
padding: 2em;
height: 12px;
}
div:hover {
background-color: grey;
}

Try substituting longtable for long_table at "Meeting Table" h5
var showImage = function showImage(id) {
var active = document.getElementById(id);
active.style.display = 'block';
var notActive = document.querySelectorAll("div:not(#" + active.id + ")");
Array.prototype.slice.call(notActive)
.forEach(function(el) {
el.style.display = "none";
})
};
div[id] {
display: none;
}
<h5 onclick="showImage('chair')">Chair</h5>
<h5 onclick="showImage('table')">Table</h5>
<h5 onclick="showImage('longtable')">Meeting Table</h5>
<div id="chair">
<img src="images/1.jpg" height="300px" alt="chair" />
<h4>Product 1</h4>
</div>
<div id="table">
<img src="images/2.jpg" height="300px" alt="table" />
<h4>Product 2</h4>
</div>
<div id="longtable">
<img src="images/3.jpg" height="300px" alt="meeting table" />
<h4>Product 3</h4>
</div>

You need to rethink the logic of your function, I'm guessing this is what you meant:
var currentID = "";
function showImage(id){
if(currentID != id){
if (currentID != "") // added this test in response to JFK's comment
document.getElementById(currentID).style.display='none';
document.getElementById(id).style.display='block';
currentID = id;
}
else { // added after OP clarified the question
document.getElementById(id).style.display='none';
currentID = "";
}
}

If you have the chance to use jQuery, there is a really awesome solution possible. It would work like this:
http://jsfiddle.net/dnf6gsuL/2/
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
<h5>Chair</h5>
<div>
<img src="images/1.jpg" height="300px"/>
<h4>Product 1</h4>
</div>
<h5>Table</h5>
<div>
<img src="images/2.jpg" height="300px"/>
<h4>Product 2</h4>
</div>
<h5 id="longtable">Meeting Table</h5>
<div>
<img src="images/3.jpg" height="300px"/>
<h4>Product 3</h4>
</div>
<script>
$("h5").click(function(eve){
$("div").each(function(){
$(this).fadeOut("fast", function(){
$(eve.target).next("div").fadeIn("fast");
});
});
});
</script>