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Fade the same image in and out in one line of CSS automatically

I have an image that I want to fade in and out automatically. I've read about transitions and animations and would like to use one or two styles (not style declarations). It's OK to start the animation via JavaScript.
In this example on MDN you can see that the items are animated on page load by switching classes. I would like it to be simpler than that.
Here is what I have so far and it seems like it should work but it's not.
function updateTransition(id) {
var myElement = document.getElementById(id);
var opacity = myElement.style.opacity;
if (opacity==null || opacity=="") opacity = 1;
myElement.style.opacity = opacity==0 && opacity!="" ? 1 : 0;
}
var id = window.setInterval(updateTransition, 5000, "myElement");
updateTransition("myElement");
#myElement {
background-color:#f3f3f3;
width:100px;
height:100px;
top:40px;
left:40px;
font-family: sans-serif;
position: relative;
animation: opacity 3s linear 1s infinite alternate;
}
<div id="myElement"></div>
Also, here is an example of an animation on infinite loop using a slide animation (3 example in the list). I'd like the same but with opacity.
https://developer.mozilla.org/en-US/docs/Web/CSS/animation
The linked question is not the same as this. As I stated, "single line styles (not style declarations)".

What you need is to define your animation using keyframes. If you are trying to apply multiple animations, you can provide a list of parameters to the animation CSS properites. Here's an example that applies a slide in and fade animation.
.fade {
width:100px;
height:100px;
background-color:red;
position:relative;
animation-name:fadeinout, slidein;
animation-duration:2s, 1s;
animation-iteration-count:infinite, 1;
animation-direction:alternate, normal;
}
#keyframes fadeinout {
0% {
opacity:0
}
100% {
opacity:100
}
}
#keyframes slidein {
from {
left:-100px;
}
to {
left:0px;
}
}
<div class='fade'>
</div>

You can use animation-iteration-count :
#myElement {
background-color: #f3f3f3;
width: 100px;
height: 100px;
top: 40px;
left: 40px;
font-family: sans-serif;
position: relative;
animation: slidein 2s linear alternate;
animation-iteration-count: infinite;
}
#keyframes slidein {
0% {
opacity: 0;
left: -100px;
}
50% {
opacity: 1;
left: 40px;
}
100% {
opacity: 0;
left: -100px;
}
}
<div id="myElement"></div>

No exit animation applied - Polymer

I have a paper-icon-button that animates (spin & opacity) when I hover an image using on-mouseenter and on-mouseleave.
The animations occur properly on-mouseenter, but the paper-icon-button simply disappears on-mouseleave rather than repeating the animation.
Can anybody help?
HTML
<img id="avatar" class="userAvatar" src="../images/hipster.png" slot="item-icon" on-mouseenter="cogSpin" on-mouseleave="cogSpin"></img>
<paper-icon-button id="cogSpin" icon="settings" class="cog" on-click="doSomething"></paper-icon-button>
CSS
.cog {
position: fixed;
color: white;
top: 129px;
left: 64px;
opacity: 0;
transition: opacity 1s, transform ease-in-out 1s;
visibility: hidden;
}
.cogOn {
visibility: visible;
opacity: 1;
transform:rotate(360deg);
}
JS
cogSpin : function() {
// css class only applied if the drawer containing it has been expanded
if(this.$.drawer.classList.contains('drawerExpand')) {
this.$.cogSpin.classList.toggle('cogOn');
}
}

That's because visibility:hidden; and it's counterpart is not an animatable CSS property. (See dev docs regarding interpolation)
Change your CSS rule to:
.cog {
position: fixed;
color: white;
top: 129px;
left: 64px;
opacity: 0;
transition: opacity 1s, transform ease-in-out 1s;
}
.cogOn {
opacity: 1;
transform:rotate(360deg);
}
The visibility property is unnecessary in any case thanks to your use of opacity.

How to control the transform distance with pure JavaScript

I made this
http://codepen.io/adamchenwei/pen/dOvJNX
and I try to apply a certain way of moving for a dom so it move for a fixed distance and stop, instead of animate and move through the whole width of the dom. However, I don't really want to fix the distance inside the css keyframe because I need to detect that distance dynamically, since my div that got animated ideally will change the width dynamically as well since that is not going always be 100% or any specific px fixed.
Is there way I can do that in JavaScript instead and not let css to take charge in this transform distance part?
Cross browser capacity will be great.
SCSS
.myItem {
height: 100px;
width: 501px;
background-color: beige;
animation: to-left-transition 300ms;
animation-iteration-count: 1;
animation-fill-mode: forwards;
animation-timing-function: ease-in-out;
}
#keyframes to-left-transition {
0% {
transform: translate(0);
}
100% {
transform: translate(100%);
}
}
HTML
<div class="myItem">
stuff here
</div>

Found out a better way. Soooooo much easier!
I should have been using transition instead of animation. As that give me the flexibility to adjust the animation accordingly.
Hope it helps someone else to save couple hours!
http://codepen.io/adamchenwei/pen/xRqYNj
HTML
<div class="myItem">
stuff here
</div>
CSS
.myItem {
position: absolute;
height: 100px;
width: 501px;
background-color: beige;
transition: transform 1s;
}
JS
setTimeout(function() {
document.getElementsByClassName('myItem')[0].style.transform="translateX(400px)";
console.log('ran');
}, 3000);

EDIT
Below is a method sugguested by Dennis Traub
setTimeout(function() {
console.log('ran');
$("head").append('<style type="text/css"></style>');
var new_stylesheet = $("head").children(':last');
new_stylesheet.html('.myItem{animation: to-left-transition 600ms;}');
}, 3000);
.myItem {
position: absolute;
height: 100px;
width: 501px;
background-color: beige;
animation-iteration-count: 1;
animation-fill-mode: forwards;
animation-timing-function: ease-in-out;
}
#keyframes to-left-transition {
0% {
transform: translate(0);
}
100% {
transform: translate(100%);
}
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="item" class="myItem">
stuff here
</div>
Answer Before EDIT
Here is a good reference for something similar to what i think you are trying to accomplish.
Based on your dynamic input you could have a function that controls how far the div transitions. Still use your code for transition in the css, but compute how far you want in the jquery or JavaScript. Then call the css transition for how far or long you want to transition.
var boxOne = document.getElementsByClassName('box')[0],
$boxTwo = $('.box:eq(1)');
document.getElementsByClassName('toggleButton')[0].onclick = function() {
if(this.innerHTML === 'Play')
{
this.innerHTML = 'Pause';
boxOne.classList.add('horizTranslate');
} else {
this.innerHTML = 'Play';
var computedStyle = window.getComputedStyle(boxOne),
marginLeft = computedStyle.getPropertyValue('margin-left');
boxOne.style.marginLeft = marginLeft;
boxOne.classList.remove('horizTranslate');
}
}
$('.toggleButton:eq(1)').on('click', function() {
if($(this).html() === 'Play')
{
$(this).html('Pause');
$boxTwo.addClass('horizTranslate');
} else {
$(this).html('Play');
var computedStyle = $boxTwo.css('margin-left');
$boxTwo.removeClass('horizTranslate');
$boxTwo.css('margin-left', computedStyle);
}
});
.box {
margin: 30px;
height: 50px;
width: 50px;
background-color: blue;
}
.box.horizTranslate {
-webkit-transition: 3s;
-moz-transition: 3s;
-ms-transition: 3s;
-o-transition: 3s;
transition: 3s;
margin-left: 100% !important;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<h3>Pure Javascript</h3>
<div class='box'></div>
<button class='toggleButton' value='play'>Play</button>
<h3>jQuery</h3>
<div class='box'></div>
<button class='toggleButton' value='play'>Play</button>
This code was written by Zach Saucier on codepen
This is a good reference for manipulating css with JS: https://css-tricks.com/controlling-css-animations-transitions-javascript/

How do I add a cycle style repeating image phase background to my website?

The question title says it all, I am not sure how to organize it in to my websites HTML due to the fixed menu bar, and its over all build. So to say, I want my website to have multiple backgrounds that fade in and out. I intend on adding more backgrounds over time. What I listed below is what I've been attempting to work with.
body {
width: 400px;
height: 400px;
}
/* set `#slideshow` parent background color */
.slideshow {
background: #000;
display:block;
width:inherit;
height:inherit;
}
#slideshow {
width: 100%;
height: 100%;
display: block;
opacity: 0.0;
background-color: #000;
/*
set background images as `url(/path/to/image)` here,
separated by commas
*/
background-image: url("http://lorempixel.com/400/400/cats/?1"),
url("http://lorempixel.com/400/400/animals/?2"),
url("http://lorempixel.com/400/400/nature/?3"),
url("http://lorempixel.com/400/400/technics/?4"),
url("http://lorempixel.com/400/400/city/?5");
background-size: cover, 0px, 0px, 0px;
/* set transtitions at 3000ms
-webkit-transition: background-image 3000ms linear;
-moz-transition: background-image 3000ms linear;
-ms-transition: background-image 3000ms linear;
-o-transition: background-image 3000ms linear;
transition: background-image 3000ms linear;
*/
}
Javascript below.
$(function() {
$.fx.interval = 0;
(function cycleBgImage(elem, bgimg) {
// `elem`:`#slideshow`
// set, reset, delay to `1000` after background image reset
elem.css("backgroundImage", bgimg)
// fade in background image
.fadeTo(3000, 1, "linear", function() {
// fade in background image
$(this).delay(3000, "fx").fadeTo(3000, 0, "linear", function() {
// split background image string at comma , creating array
var img = $(this).css("backgroundImage").split(","),
// concat first background image to `img` array,
// remove first background image from `img` array
bgimg = img.concat(img[0]).splice(1).join(",");
// recursively call `cycleBgImage`
cycleBgImage(elem, bgimg);
});
});
}($("#slideshow")));
});
The division script, which I'm not sure I have a use for unless I make my whole website one large div which seems pointless.
<div class="slideshow">

Here is a quick hack. I would probably do something more elegant with management of the images in an array, but this should get you going.
function swap(){
var $targets = $("#slideshow img");
var className = "active";
var $next = $targets.filter(".active").next();
if ($next.length === 0) { $next = $targets.first(); }
$targets.removeClass(className);
$next.addClass(className)
}
swap();
window.setInterval(swap, 5 * 1000);
#slideshow {
background-color: #000;
width: 400px;
height: 400px;
border: solid 1px;
overflow: hidden;
position: relative;
}
#slideshow img {
position:absolute;
opacity: 0;
transition: opacity 2s ease-in-out;
}
#slideshow img.active {
opacity: 1;
}
<div id="slideshow">
<img src="http://lorempixel.com/400/400/cats/?1" />
<img src="http://lorempixel.com/400/400/animals/?2" />
<img src="http://lorempixel.com/400/400/nature/?3" />
<img src="http://lorempixel.com/400/400/technics/?4" />
<img src="http://lorempixel.com/400/400/city/?5" />
</div>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

How to add css transitions to js scroll in header?

I have a header that appears when the page scrolls down. I am trying to add css transitions to make it fade in and out because I've read that using javascript for fading is not as efficient.
.header-wrapper {
top:0;
left:0;
right:0;
position: fixed;
display:none;
height: 60px;
border-top: 1px solid #000;
background: red;
z-index: 1;
}
.header-wrapper.active {
display:block;
}
.header {
background-color:#000;
height:80px;
}
Here is the js fiddle
$(window).scroll(function () {
var y = $(window).scrollTop();
// if above 300 and doesn't have active class yet
if (y > 300 && !$('.header-wrapper').hasClass('active')) {
$('.header-wrapper').addClass('active');
// if below 300 has still has active class
} else if(y <= 300 && $('.header-wrapper').hasClass('active')) {
$('.header-wrapper').removeClass('active');
}
});

Transitions are added with the css3 property transition.
One common reason for confusion: you can only transition properties that accept numeric values. Thus, you can't transition between display: block and display: none.
However you can transition between opacity: 0 and opacity: 1 with:
transition: 0.5s opacity
That would look something like this:
.bottomMenu {
...
opacity: 0;
transition: 0.5s opacity;
...
}
.bottomMenu.active {
opacity: 1;
}
For your particular case, I might recommend transitioning the height between 0 and 60px.
For that you can use:
transition: 0.5s height
So:
.bottomMenu {
...
height: 0;
transition: 0.5s height;
...
}
.bottomMenu.active {
height: 80px;
}

To animate the opacity the element must be visible. So remove the display:none and make it fully transparent (opacity:0). You can then use CSS transitions to animate the opacity when the classname changes:
.bottomMenu {
...
display:block;
opacity: 0;
transition: opacity .25s ease-in-out;
-moz-transition: opacity .25s ease-in-out;
-webkit-transition: opacity .25s ease-in-out;
}
.bottomMenu.active {
opacity:1
}
http://jsfiddle.net/oL9ro4gL/6/
Furthermore, you're not restricted to just animating the opacity:
.bottomMenu {
...
transition: all .25s ease-in-out;
}
.bottomMenu.active {
opacity:1;
height: 60px;
background-color: blue;
transform:rotate(180deg);
color:white;
font-size:40px;
etc...
}
http://jsfiddle.net/oL9ro4gL/8/

Unfortunately, you can't animate the display property. See this question and its suggestions for workarounds.