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Show div when scrolling using vanilla JavaScript

I'm using vanilla JavaScript and would like to figure out a way where a div container is hidden, but when the user scrolls to 50% of the div container, that's when the div is fully visible. Kind of like a fading-in effect. This is what I have so far:
// delays scroll affects
function debounce(func, wait = 20, immediate = true) {
var timeout;
return function() {
var context = this,
args = arguments;
var later = function() {
timeout = null;
if (!immediate) func.apply(context, args);
};
var callNow = immediate && !timeout;
clearTimeout(timeout);
timeout = setTimeout(later, wait);
if (callNow) func.apply(context, args);
};
}
// adds animation for section cards
function cardActive(e) {
const cards = document.querySelectorAll('.slide-in');
// checks if image is half shown from bottom
cards.forEach(card => {
const slideInAt = (window.scrollY + window.innerHeight) - card.height / 2;
if (slideInAt > card.offsetTop) {
card.classList.add('active')
} else {
card.classList.remove('active');
}
})
};
window.addEventListener('scroll', debounce(cardActive));
.slide-in {
opacity: 50%;
transition: opacity 0.8s;
}
.slide-in.active {
transition: opacity 0.8s;
opacity: 100%;
visibility: visible !important;
}
.placeholder {
margin-top: 400px;
}
.icon {
width: 100px;
}
<div class="placeholder"></div>
<div class="mission-1 slide-in">
<div class="section-card">
<img class="icon" src="https://image.flaticon.com/icons/svg/869/869767.svg" alt="icon">
<h6 class="mission-card-title">Title 1</h6>
<p class="p-special">Lorem Ipsum.</p>
</div>
</div>
<div class="placeholder"></div>

You need to make two small changes:
You need to replace card.height with card.offsetHeight in your JS file.
Use transition in your CSS file, you do not need animation for a fade in effect:
.slide-in {
opacity: 0%;
transition: opacity 0.8s;
}
.active {
transition: opacity 0.8s;
opacity: 100%;
visibility: visible !important;
}

Here the image is already shown with opacity 1 and then once scrolled over it it will fade using just JS.
// adds animation for section cards
window.addEventListener('scroll', (e) => {
last_known_scroll_position = window.scrollY;
let img = document.getElementById("img-1");
if(img.offsetTop < last_known_scroll_position){
img.style.opacity= 0.1;
}else{
img.style.opacity= 1;
}
});
.slide-in {
opacity: 50%;
}
.slide-in.active {
opacity: 100%;
-webkit-animation: animat_show 0.8s;
animation: animat_show 0.8s;
visibility: visible !important;
}
.lorem {
margin-bottom: 500px;
}
img {
width: 500px;
}
<section class="space">
<p class="lorem">lorem ipsum</p>
<div class="slide-in">
<img class="img-1" id="img-1" src="https://image.flaticon.com/icons/svg/869/869767.svg" alt="confetti">
</div>
<p class="lorem">lorem ipsum</p>
</section>

adding fadein effect with inner.HTML

Looking to fade-in content when using inner.HTML.
Current code;
<td style="width: 20%;" class="responsive-td" valign="top">
<div id="placeholder1" class="placeholder1" style="color:white;"></div>
</td>
if (//logic here){
document.getElementById('placeholder1').innerHTML ='add this with fading effect';
setTimeout(addFn1, 300);
function addFn1() {
document.getElementById('placeholder2').innerHTML ='add this with fading effect';}
setTimeout(addFn2, 1200);
function addFn2() {
document.getElementById('placeholder3').innerHTML ='add this with fading effect';}
}
I attempted using css however it doesn't create the effect due to setTimeout.
Is there a simple solution using CSS or JS? Or even jQuery if need be?

That is easy to do with jQuery, since there are methods for simple animations like this.
Have a look at .fadeIn() and .fadeOut().
if (true){
$('#placeholder1').html('add this with fading effect').fadeIn(600);
setTimeout(addFn1, 300);
function addFn1() {
$('#placeholder2').html('add this with fading effect').fadeIn(600);}
setTimeout(addFn2, 1200);
function addFn2() {
$('#placeholder3').html('add this with fading effect').fadeIn(600);}
}
body{
background-color:black;
}
.placeholder1{
display:none;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<td style="width: 20%;" class="responsive-td" valign="top">
<div id="placeholder1" class="placeholder1" style="color:white;"></div>
<div id="placeholder2" class="placeholder1" style="color:white;"></div>
<div id="placeholder3" class="placeholder1" style="color:white;"></div>
</td>

May be you can try using opacity set to old=zero to new=one while changing text.
Option: Using CSS3 and Js(no jquery)
document.addEventListener('DOMContentLoaded', function() {
var quotes = ["Hello", "there", "everyone"];
var infos = document.querySelectorAll('div.info');
var repeat = Array.prototype.slice;
var fadeIn = function(i) {
if (!infos[i]) {
return;
}
infos[i].innerHTML = quotes[i];
infos[i].classList.add("open");
};
repeat.call(infos).forEach(function(el) {
var callBack = function(e) {
var that = this;
repeat.call(infos).forEach(function(cur, ind) {
if (cur == that) {
fadeIn(1 + ind);
return false;
}
});
};
el.addEventListener('webkitAnimationEnd', callBack);
el.addEventListener('animationEnd', callBack);
});
fadeIn(0); /* trigger fade */
});
.info {
opacity: 0;
filter: alpha(0%);
border: 1px solid #ccc;
margin: 1px 2px;
}
#keyframes fade {
from {
opacity: 0;
filter: alpha(0%);
}
to {
opacity: 1;
filter: alpha(100%);
}
}
.info.open {
-webkit-animation: fade .3s;
-moz-animation: fade .3s;
-ms-animation: fade .3s;
-o-animation: fade .3s;
animation: fade .3s;
opacity: 1;
filter: alpha(100%);
}
<div class="info"></div>
<div class="info"></div>
<div class="info"></div>

How I can animate this slideshow(by changing its src)?

Okay okay, so before marking this post as repeated. Let me explain to you:
I made a slideshow in javascript(Vue) and it works by changing its src in an object every time I press a button(next)
It works and all but the problem is that it doesn't get animated no matter what I do, I made a transition on them, set timeout function on it...etc and nothing even the smallest worked.
I could have made another idea which works by the position absolute but I don't want to do that because it will take a loot of time and it will be extremely buggy as position absolute ruins it. So any help on this please?
<template>
<main>
<div id="slideshow">
<figure id="pics">
<img id="slidepic" v-bind:src="pictures[count].src">
<figcaption>{{pictures[count].alt}}</figcaption>
</figure>
</div>
<p>{{count+1}}/{{pictures.length}}</p>
<div id="controls">
<div #click="move(-1)">Previous</div>
<div #click="move(1)">Next</div>
</div>
</main>
Javascript:
methods: {
move: function(num) {
let slideimg = document.querySelector("#slidepic");
slideimg.classList.add("fadeOut");
this.count += num;
if (this.count < 0) {
this.count = this.pictures.length - 1;
} else if (this.count >= this.pictures.length) {
this.count = 0;
}
setTimeout(function() {
slideimg.src = this.pictures[1].src;
}, 1000);
}
}
CSS:
#pics {
opacity: 0.5s;
transition: 0.5s;
}
#pics.fadeOut {
opacity: 1;
}
I didn't include the object(that is in data object, something in Vue) because it would be useless in this situation.

First off all it's transition: <property-name> 0.5s linear; and not transition: 0.5s;. See the transition documentation.
There is no animation for changing the src of an image (see list of animatable css properties).
To do something like this, you can stack all your images into one element and then use css animations and the transform property to create a carousel
var next = document.getElementById('next');
var prev = document.getElementById('prev');
var slideshow = document.getElementById('slideshow');
next.onclick = function() {
var lastChild = slideshow.children[slideshow.children.length - 1];
var firstChild = slideshow.children[0];
var activeEle = document.querySelector('.item.active');
var nextEle = document.querySelector('.item.next');
var prevEle = document.querySelector('.item.prev');
activeEle.classList.remove('active');
activeEle.classList.add('prev');
nextEle.classList.add('active');
nextEle.classList.remove('next');
prevEle.classList.remove('prev');
if (nextEle.nextElementSibling) {
nextEle.nextElementSibling.classList.add('next');
} else {
firstChild.classList.add('next');
}
};
prev.onclick = function() {
var lastChild = slideshow.children[slideshow.children.length - 1];
var activeEle = document.querySelector('.item.active');
var nextEle = document.querySelector('.item.next');
var prevEle = document.querySelector('.item.prev');
// Move the .active class to the previous element
activeEle.classList.remove('active');
activeEle.classList.add('next');
prevEle.classList.add('active');
prevEle.classList.remove('prev');
nextEle.classList.remove('next');
if (prevEle.nextElementSibling) {
prevEle.nextElementSibling.classList.add('prev');
} else {
lastChild.classList.add('prev');
}
};
#slideshow {
width: 100px;
height: 100px;
overflow: hidden;
position: relative;
}
.item {
width: 100%;
height: 100%;
color: white;
background-color: blue;
position: absolute;
/*display: none;*/
top: 0;
left: 0;
z-index: -100;
transition: translateX(-100%);
transition: transform .5s ease-in-out;
opacity: 0;
}
.active {
opacity: 1;
display: block;
z-index: 1;
transform: translateX(0);
}
.next {
transform: translateX(200%);
z-index: 1;
}
.prev {
transform: translateX(-100%);
opacity: 1;
z-index: 1;
}
<div id="slideshow">
<div class="item active">1</div>
<div class="item next">2</div>
<div class="item">3</div>
<div class="item">4</div>
<div class="item">5</div>
<div class="item">6</div>
<div class="item prev">7</div>
</div>
<button type="button" id="prev">Prev</button><button type="button" id="next">Next</button>

As you mention you want to build a slideshow on Vue JS, and because jQuery on top of Vue is not recommended, I suggest that you try Vueper Slides, available on NPM. Unless it is for a learning purpose.

I have created two solutions.
First of all. You've a typo.
#pics {
opacity: 0.5s; // <--- remove "s"
transition: 0.5s; // <--- and forgot the property-name (all, opacity ...)
}
#pics.fadeOut {
opacity: 1;
}
I commented all lines I've changed.
Solution
<template>
<main>
<div id="slideshow">
<!--
I recommend to you ref inestad of querySelector.
https://vuejs.org/v2/api/#ref
I've used the v-bind shorthand.
-->
<figure id="pics1" ref="pics1">
<img id="slidepic" :src="pictures[count].src">
<figcaption>{{pictures[count].alt}}</figcaption>
</figure>
<!--
VueJS build-in transition element.
You have to add a key attribute to detect that the content has changed.
I recommend to use this instead of your solution.
It's easier to implement, no class add/remove struggle, its a part of vue, you can add hooks etc.
https://vuejs.org/v2/guide/transitions.html
-->
<transition tag="figure" name="fade" ref="pics2">
<figure id="pics2" :key="`figure-${count}`">
<img :src="pictures[count].src">
<figcaption>{{pictures[count].alt}}</figcaption>
</figure>
</transition>
</div>
<p>{{count+1}}/{{pictures.length}}</p>
<div id="controls">
<div #click="move(-1)">Previous</div>
<div #click="move(1)">Next</div>
</div>
</main>
</template>
<script>
export default {
name: 'teams',
data() {
return {
count: 0,
pictures: [
{
src: 'https://picsum.photos/200/300',
alt: 'test'
},
{
src: 'https://picsum.photos/200/400',
alt: 'test2'
}
]
};
},
methods: {
// instead of move: function(num) {} you can also write move() {}
move(num) {
this.count += num;
if (this.count < 0) {
this.count = this.pictures.length - 1;
} else if (this.count >= this.pictures.length) {
this.count = 0;
}
}
},
// Watch "count" changes and add or remove classes
// you can also add this to your "move" method
watch: {
count() {
// access the reference
const element = this.$refs.pics1;
element.classList.add('fadeOut');
element.classList.remove('fadeIn');
setTimeout(() => {
element.classList.remove('fadeOut');
element.classList.add('fadeIn');
}, 500); // same duration as css transition
}
}
};
</script>
<style scoped lang="scss">
#pics1 {
opacity: 1;
transition: opacity 0.5s;
}
#pics1.fadeIn {
opacity: 1;
}
#pics1.fadeOut {
opacity: 0;
}
// All classes for <transition>
// There are all automatically used by vue
.fade-enter-active {
transition: opacity 0.5s;
}
.fade-leave {
display: none;
}
.fade-enter,
.fade-leave-to {
opacity: 0;
}
</style>

Animating from display none using JS Promises

I am trying animating an element which has display property set to null. Objective is to recreate something that bootstrap does in modal.
Further Explanation:
An element which is set to display none on page load but when a user clicks a certain button it shows up with animation (fade in for example). Then when user click on close button or that button again it fades out and its display property is set to none again.
Problem:
When box display property is set to none. And i click on the button. It's display is set to block and adding class "Show" both occur simultaneously and instantaneously so element just shows rather than animating
Here is my Code:
HTML:
<button id="btn">Show / Hide</button>
<div id="box" class="show">
</div>
CSS:
#box {
background-color: aquamarine;
height: 100px;
width: 100px;
opacity: 0;
transition: ease all 0.3s;
}
#box.show {
transition: ease all 0.3s;
opacity: 1;
}
Javascript:
var box = document.querySelector("#box");
var btn = document.querySelector("#btn");
box.style.display = "none"
btn.addEventListener("click", function () {
if(box.style.display == "none") {
return new Promise(function(resolve, reject) {
box.style.display = "block";
resolve();
}).then(function() {
box.classList.add('show');
});
} else if(box.style.display == "block") {
return new Promise(function(resolve, reject) {
box.addEventListener('transitionend', function () {
box.style.display = "none";
})
resolve();
}).then(function() {
box.classList.remove('show');
});
}
});
JSFiddle: https://jsfiddle.net/ptLggbmb/1/

Instead of using Promises you could simply use the transitionend listener and for the fadeIn animation force a layout/reflow before applying the class to the box.
var box = document.querySelector("#box");
var btn = document.querySelector("#btn");
btn.addEventListener("click", function() {
var prevDisplay = box.style.display;
var listener = function() {
box.style.display = "none";
removeListener(listener);
};
if (prevDisplay !== "none") {
addListener(listener);
box.classList.remove('show');
} else {
removeListener(listener);
box.style.display = null;
box.offsetLeft;
box.classList.add('show');
}
function addListener(fn) {
box.addEventListener('transitionend', fn);
}
function removeListener(fn) {
box.removeEventListener('transitionend', fn);
}
});
#box {
background-color: aquamarine;
height: 100px;
width: 100px;
opacity: 0;
transition: ease all 0.3s;
}
#box.show {
transition: ease all 0.3s;
opacity: 1;
}
<button id="btn">Show / Hide</button>
<div id="box" class="show">
</div>

I think you overcomplicated this to the extreme, IMHO. Try this (Pure CSS with a simple JS toggle of classes):
https://jsfiddle.net/ptLggbmb/17/
HTML:
<button id="btn">Show / Hide</button>
<div id="box" class="show">
CSS:
#box {
background-color: aquamarine;
height: 100px;
width: 100px;
opacity: 0;
display: none;
transition: ease all 1s;
}
#box.show {
display: block;
opacity: 1;
}
JS:
var box = document.querySelector("#box");
var btn = document.querySelector("#btn");
btn.addEventListener("click", function () {
box.classList.toggle('show');
});

Show element for a second, then hide it

I'm trying to show an element for a short amount of time, then hiding it with a CSS transition, on a button click.
Here's the outline of what I did.
elem has a property of opacity: 0.
Fire event when button gets selected.
The events function will add, then remove a class named show to elem.
CSS has the following property: transition: opacity 500ms ease 1000ms;.
#elem.show has a property of opacity: 1.
The problem is, nothing happens when the button gets clicked on. How can I make element get shown, without a transition effect, then, after 1s close with a transition?
JSFiddle
var btn = document.getElementById('btn');
var elem = document.getElementById('elem');
btn.addEventListener('click', function() {
elem.classList.add('show');
elem.classList.remove('show');
});
#elem {
background-color: orange;
width: 100px;
height: 100px;
opacity: 0;
transition: opacity 500ms ease 1000ms;
}
#elem.show {
opacity: 1;
transition: none;
}
<button id="btn">Press Me</button>
<div id="elem"></div>

Using setTimeout is not tidy - it is better to listen to the animation end event and remove the show class. I have also used animation to show and hide the element successively - see demo below:
var btn = document.getElementById('btn');
var elem = document.getElementById('elem');
btn.addEventListener('click', function() {
elem.classList.remove('show');
// this force-restarts the CSS animation
void elem.offsetWidth;
elem.classList.add('show');
});
elem.addEventListener("animationend", function(){
elem.classList.remove('show');
}, false);
#elem {
background-color: orange;
width: 100px;
height: 100px;
opacity: 0;
}
#elem.show {
animation: anime 1s 1;
}
#keyframes anime {
0% {
opacity: 1;
}
50% {
opacity: 1;
}
100% {
opacity: 0;
}
}
<button id="btn">Press Me</button>
<div id="elem"></div>
Update
Listening to the animation-end event do not seem necessary actually - it works properly even without it. The gist here is the use of void elem.offsetWidth to forcefully restart the animation:
var btn = document.getElementById('btn');
var elem = document.getElementById('elem');
btn.addEventListener('click', function() {
elem.classList.remove('show');
// this force-restarts the CSS animation
void elem.offsetWidth;
elem.classList.add('show');
});
#elem {
background-color: orange;
width: 100px;
height: 100px;
opacity: 0;
}
#elem.show {
animation: anime 1s 1;
}
#keyframes anime {
0% {
opacity: 1;
}
50% {
opacity: 1;
}
100% {
opacity: 0;
}
}
<button id="btn">Press Me</button>
<div id="elem"></div>

just do this :
setTimeout(function() { elem.classList.remove('show'); }, 1000);
instead of writing :
elem.classList.remove('show');
To handle repeated clicks, do this ::
var btn = document.getElementById('btn');
var elem = document.getElementById('elem');
var timeOutFunc;
btn.addEventListener('click', function() {
elem.classList.add('show');
clearTimeout(timeOutFunc);
timeOutFunc = setTimeout(function() {elem.classList.remove('show') } , 1000);
});

This borrows from other answers, and addresses the multiple press "issue"
var btn = document.getElementById('btn');
var elem = document.getElementById('elem');
btn.addEventListener('click', (function() {
var timer = null;
return function() {
elem.classList.add('show');
if (timer) {
clearTimeout(timer);
timer = null;
}
timer = setTimeout(e => elem.classList.remove('show'), 1000);
};
})());
#elem {
background-color: orange;
width: 100px;
height: 100px;
opacity: 0;
transition: opacity 500ms ease 500ms;
}
#elem.show {
opacity: 1;
transition: none;
}
<button id="btn">Press Me</button>
<div id="elem"></div>

Try with this...i Hope its resolved your prblm
https://jsfiddle.net/b3en368p/5/
var btn = document.getElementById('btn');
var elem = document.getElementById('elem');
btn.addEventListener('click', function() {
elem.classList.add('show');
setTimeout(function(text){
elem.classList.remove('show');
}, 1000);
});

Add css
#elem {
background-color: orange;
width: 100px;
height: 100px;
display: none;
}
#elem.show {
display: block;
}
Your listener should be like this-
btn.addEventListener('click', function() {
elem.classList.add('show');
setTimeout(function(){
elem.classList.remove('show');
}, 1000);
});