Pure Javascript alternatives to toggling a CSS class? - javascript

My goal is to rotate a div 180deg on each click, without toggling CSS classes.
I can achieve one rotation with the first click (.style.transform =
"rotate(180deg)";), but any subsequent click has no effect.
BTW, why exactly is that? The div's Id hasn't changed, so, in theory, the same trigger (a click, in this case) should call the same function, right? But it doesn't. I wonder what's the logic here, what's the technical explanation, and, moving to practice, how can I further manipulate this post-div (that is, the original div after its JavaScript manipulation) -- again, without toggling CSS classes.
function rotate() {
document.getElementById("container").style.transform =
"rotate(180deg)";
}
.container {
width: 200px;
height: 400px;
border: 5px solid;
border-bottom-color: blue;
border-top-color: red;
}
<div class="container" id="container" onclick="rotate()"></div>

The first time you change the transformation from "" to "rotate(180deg)", so it rotates.
Subsequent times you change it from "rotate(180deg)" to "rotate(180deg)" … which isn't a change at all, so nothing happens.
If you want to change it, then you need to actually assign a different value to it.
e.g.
const style = document.getElementById("container").style;
if (style.transform) {
style.transform = "";
} else {
style.transform = "rotate(180deg)";
}
Toggling a class is simpler, and clearer.
document.querySelector("#container").addEventListener("click", e => e.currentTarget.classList.toggle("rotated"));
.container {
width: 200px;
height: 400px;
border: 5px solid;
border-bottom-color: blue;
border-top-color: red;
transition: transform 0.25s;
}
.rotated {
transform: rotate(180deg);
}
<div class="container" id="container"></div>

You need to check the transform value and then rotate it anti-clockwise.
Here is the code:
HTML
<div class="container" id="container" onclick="rotate()"></div>
CSS
.container {
width: 200px;
height: 400px;
border: 5px solid;
border-bottom-color: blue;
border-top-color: red;
}
JS
function rotate() {
document.getElementById("container").style.transform =
document.getElementById("container").style.transform ===
"rotate(180deg)" ? "rotate(0deg)" : "rotate(180deg)";
}
Here is an example in codepen

The reason why the div is not rotating after first function call is that you are setting the transform style property to constant value (180deg). After first call the transform is performed and all following calls set transform to exactly the same value. In order to make it work, you have to increment rotate property each time you call the function.
In example:
let rotation = 0;
function rotate() {
document.getElementById("container").style.transform = `rotate(${rotation}deg)`;
rotation = (rotation + 180) % 360;
}

I made a fiddle , but basically, you can't rotate for the same value. Of course this is very raw, but prove the concept for you to understand. You can do it more programatically of course.
document.getElementById('container').addEventListener('click', function () {
this.style.transform = this.style.transform == "rotate(180deg)" ? "rotate(-90deg)" : "rotate(180deg)";
}
);
You can check this out: tutorial

<script>
var degrees = 0;
function rotate() {
if(degrees == 180){
document.getElementById("container").style.transform =
"rotate(360deg)";
degrees= 0;
}else{
document.getElementById("container").style.transform =
"rotate(180deg)";
degrees= 180;
}
}
</script>
Clearly is not optimized but could help you.
JSFiddle here

Others have answered your question already, so I will provide with an example to make your code a little bit more dynamic.
/**
* Rotate an <element> with a certain angle <rotateBy>
* 'this' is a reference to itself, which is passed by as an argument from the HTML.
* Change '180' in the method call to whatever to have it rotate differently.
*/
function rotate(element, rotateBy) {
var currentRotation = element.rotation || 0; // default to zero if not existing
newRotation = rotateBy + currentRotation;
element.rotation = newRotation; // store the property in the element
element.style.transform = "rotate(" + newRotation + "deg)";
}
.container {
width: 200px;
height: 400px;
border: 5px solid;
border-bottom-color: blue;
border-top-color: red;
transition: transform 400ms;
}
<div class="container" onclick="rotate(this, 180)"
></div>

Related

CSS incrementing transition animation on every button click

Given
var box = document.querySelector('.box');
document.addEventListener("click", (event) => {
if (!event.target.closest("button")) return;
if(event.target.id === "button") {
box.classList.add('move');
}
});
.box {
width: 100px;
height: 100px;
background-color: #000;
transition: transform 1s;
}
.move {
transform: translateX(20px);
}
<div class="box"></div>
<button id="button">button</button>
with a JS Fiddle here.
I want the box's x-position to increment by 20px on every button click.
I am not sure how to proceed. I initially tried using #KeyForms but that requires the from and to prefixes, on which I cannot (I think) add a variable value. Same issue arises here, it seems I cannot have a variable in the css code which I can increment. Am I using the correct function at all (transition) ?
I also tried
if(event.target.id === "button") {
if(!box.classList.contains('open')){
box.classList.add('open');
}else {
box.classList.remove('open');
}
}
but that seems to move the box back and forth repetitively.
Does anyone have any tips or ideas? (I am adding the Javascript tag, since I suspect this problem may potentially be solved in JS directly).
You can store the x position in a variable, increment by 20 every click and apply it to the transform style property:
var x = 0, box = document.querySelector('.box');
button.addEventListener('click', function() {
x += 20, box.style.transform = `translateX(${x}px)`;
})
.box {
width: 100px;
height: 100px;
background-color: #000;
transition: 1s;
}
<div class="box"></div>
<button id="button">button</button>
Just keep on adding Using javascript style
var button = document.querySelector('#button');
button.onclick = function () {
document.querySelector('.box').style.transform += "translateX(20px)";
};
.box {
width: 100px;
height: 100px;
background-color: #000;
transition: transform 1s;
}
<div class="box"></div>
<button id="button">button</button>
Using javascript style would answer your question. There is CSS style for javascript like box.style.transform = 'translateX(20px)'. In Javascript you can calculate styles values(Of course in CSS changing values with calculating is possible). So I added some codes like below.
var box = document.querySelector('.box');
let cnt = 0;
document.addEventListener("click", (event) => {
if (!event.target.closest("button")) return;
if(event.target.id === "button") {
console.log(box.style.transform)
cnt++;
console.log(cnt)
box.style.transform = `translateX(${20 * cnt}px)`;
}
});
.box {
width: 100px;
height: 100px;
background-color: #000;
transition: transform 1s;
}
.move {
transform: translateX(20px);
}
.move1 {
transform: translateX(-20px);
}
<div class="box"></div>
<button id="button">button</button>

JS code to change parameter 'top' on click

Here is the pen I've created.
HTML
<div class = 'cc'>
<div class = 'bb'><div class = 'aa'> Some word </div></div>
</div>
CSS
.cc {
width: 100%;
min-height: 90px;
margin: 0;
padding: 0;
border: 1px solid #999999;
border-radius: 3px;
padding-left: 20px;
padding-right: 20px;
font-family: "Calibri";
font-size: 17px;
color: #666666;
background-color: rgba(0,0,0,.0);
}
.bb {
height: 100px;
width: 100%;
background-color: rgba(0,0,0,.5);
}
.aa {
position: relative;
top: 50%;
transform: translateY(-50%);
}
Now I want to create a clickable event such that when user click on class bb, page will check the top parameter of class aa - if it is 50% then smoothly change that to 10% and vice versa.
I want to use JavaScript code to achieve that. How can I do that?
hey just tried to gave shot at it , seems its working please look into this
let bb = document.querySelector('.bb');
let aa = document.querySelector('.aa');
bb.addEventListener('click',e => {
let top = window.getComputedStyle(aa).getPropertyValue('top');
if(top === '50px'){
aa.style.top = '10%';
}else{
aa.style.top = '50%';
}
})
Got it. It is tested and it seems to work.
let bb = document.querySelector('.bb');
let aa = document.querySelector('.aa');
bb.addEventListener('click', function(){
if(window.getComputedStyle(aa).getPropertyValue('top') === '50px'){
aa.style.top = '10%';
}else{
aa.style.top = '50%';
}
})
First, I used querySelector to get .bb and .aa.
Then, I added a event listener to bb.
Next, in the event listener I used window.getComputedStyle(), got the value of top from it and checked if it is 50px.
Last of all, if it is, change that to 10%, else change it to 50%.
I did this on CodePen, you can check it here (notice I changed the style from gray to white because gray is hard to read inside a black box).

Position not changed by animation

This question is about SVG.js
I use two move commands on animations of two SVG objects to swap their positions. I then use a callback from afterAll to move one of these objects further. I find that I need to specify my new position relative the the previous changes, i.e. from the position of the object right at the start. This is a headache, for keeping track of old coordinate changes (deltas).
So:
do I need to "commit" (or finish) my animation to change the object position permanently, before moving on? How?
am I accidentally re-using the FX object by calling animation() again on the same object at a different part in the code?
Thanks for any help...
If you just want to swap SVG images maybe you don't need a library (A and B options)
A) To do so you can rely on basic CSS transition.
div {
position: absolute;
width: 100px;
height: 100px;
}
#one {
background-color: #39464e;
left: 0;
}
#two {
background-color: #ff4f68;
right: 0;
}
body.swap #one {
left: calc(100% - 100px);
transition: 5s;
}
body.swap #two {
right: calc(100% - 100px);
transition: 5s;
}
Example: https://jsfiddle.net/gengns/et9dbpur/
You can use a svg tag instead of a div or set your SVG in a div background-image.
B) If you don't want to animate, just simple swap them you can do it in a declarative way with CSS Grid.
body {
display: grid;
grid-template-areas: 'one two';
}
body.swap {
grid-template-areas: 'two one';
}
div {
width: 100px;
height: 100px;
}
#one {
background-color: #39464e;
grid-area: one;
}
#two {
background-color: #ff4f68;
grid-area: two;
}
Example: https://jsfiddle.net/gengns/bsacypd8/
C) Using svg.js 2.7.1
SVG.on(document, 'DOMContentLoaded', function() {
const draw = SVG('drawing')
// Rectangles
const rect_one = draw.rect(100, 100).attr({fill: '#39464e'})
const rect_two = draw.rect(100, 100).attr({fill: '#ff4f68'}).move(500, 0)
// Swap
rect_one.animate().move(500, 0)
rect_two.animate().move(0, 0).after(() => {
// Swap again
rect_one.animate().move(0, 0)
rect_two.animate().move(500, 0)
})
})
Example: https://jsfiddle.net/gengns/497j1z0a/
Hope this help :)

How to fetch the background of DIV on a bottom layer with exact position using jQuery and CSS

I'm looking to make a page that has a background gradient that changes color every few seconds and blends between transitions. Now I want to apply this effect on the to the upper elements that are blocked by a element that has a solid background.
To give you a better example what I mean I have attached a simple mockup and hopefully your understand what I'm attempting to do, I'm open to suggestions.
(source: bybe.net)
The problem is obviously the block that contains the black background which any PNG transparent used would see black not the gradient.
I'll include sample code so far:
<body><!-- A Jquery script will be used to add CSS background, Easy stuff -->
<div class="blackbox">
<div class="logo"><img src="#" alt=""></div>
<hr class="h-line">
<div class="v-line"> </div>
</div>
So what I'm after is either:
A known jQuery method to obtain a background image but it needs to be able to refer of the position of the gradient so its inline with the background.
A better solution to getting this to work, please bare in mind that the page needs to be responsive so I could use other methods but since its responsive I can't think of any.
Since you ask for alternatives to jQuery solutions
You could play a little with margins and box-shadow and keyframe animations.
Something in this direction for the shape (depends on what you want to do with which part - add content ... and in what way you want it to be responsive):
html:
<div class="wrapper">
<div class="header"><img src="http://i.imgur.com/CUbOIxr.png" alt="Company name" /></div>
<div class="content"></div>
</div>
CSS:
body {
background:orange;
width:100%;
height:100%;
}
.wrapper {
width:40%;
height:90%;
border:30px solid #000;
border-right-width:100px;
border-bottom-width:100px;
}
.header {
width:100%;
border-bottom:10px solid transparent;
-webkit-box-shadow: 0 30px 0 #000;
-moz-box-shadow: 0 30px 0 #000;
box-shadow: 0 30px 0 #000;
}
.header img {
width:100%;
}
.content {
width:95%;
height:400px;
background-color:#000;
margin-top:30px;
}
DEMO
This way no javascript is needed. And for the background you can use a linear gradient and do all animations with css transitions or keyframe animations. You also need to play with the lengths and adjust the borders and box-shadows to your needs, maybe add some #media queries for the responsiveness.
Hope this helps you a little in the right direction =)
Update:
I hoped the gradients changing was the smaller problem ;-) Silly me, sorry.
I will elaborate my CSS-only suggestion for the animation, but you can choose a javascript slider for the background animation, if you don't like CSS3 solutions - although this is the hot stuff now ;-)
Ok. So, I would add some more fixed positioned elements with gradient backgrounds (layer1 and layer2).
To have something in this direction in the html now:
<div class="layer layer1"></div>
<div class="layer layer2"></div>
<div class="wrapper">
<div class="header">
<img src="http://newtpond.com/test/company-name.png" alt="Company name" />
</div>
<div class="content"></div>
</div>
and add a keyframe animation on them in CSS (here it is just with the -webkit vendor prefix [probably cause I am a lazy bum], but I hope you can get the idea, and could add the others):
body {
width:100%;
height:100%;
margin:0;
padding:0;
}
/* for the animation */
.layer {
position:fixed;
width:100%;
height:100%;
}
#-webkit-keyframes GoLayer1 {
0% {
opacity:1;
}
50% {
opacity:0;
}
100% {
opacity:1;
}
}
#-webkit-keyframes GoLayer2 {
0% {
opacity:0;
}
50% {
opacity:1;
}
100% {
opacity:0;
}
}
.layer1 {
background: -webkit-linear-gradient(bottom, rgb(43, 70, 94) 29%, rgb(194, 41, 41) 65%, rgb(155, 171, 38) 83%);
-webkit-animation: GoLayer1 5s infinite;
}
.layer2 {
background: -webkit-linear-gradient(bottom, rgb(225, 202, 230) 29%, rgb(39, 163, 194) 65%, rgb(36, 124, 171) 83%);
-webkit-animation: GoLayer2 5s infinite;
}
/* the wrapper shape */
.wrapper {
z-index:999;
opacity:1;
position:relative;
width:40%;
height:90%;
border:30px solid #000;
border-right-width:100px;
border-bottom-width:100px;
}
.header {
width:100%;
border-bottom:10px solid transparent;
-webkit-box-shadow: 0 30px 0 #000;
-moz-box-shadow: 0 30px 0 #000;
box-shadow: 0 30px 0 #000;
}
.header img {
width:100%;
}
.content {
width:95%;
height:400px;
background-color:#000;
margin-top:28px;
}
DEMO (tested in Chrome 26 - looked cool =)
This is now where I can point you according this CSS-only approach. There is still stuff to modify and consider browser compatibility. But it is certainly an alternative ... and a step in the direction where html5 and css3 is going (if you want to be hot and cool ;-), hehe, sorry, too much silliness.
Good luck!
Update 2:
So, I overcame my laziness a tiny bit and added some more vendor prefixes to the top example (and of course you can use any image as background):
DEMO
And here I add another example, that is using a png image for the gradient, and is sliding up and down in the background (as another alternative):
DEMO
There are many ways to do this, CSS3 and images are already suggested, so I'll suggest using a canvas.
The HTML canvas element has everything you need built in. It allows for gradient background fills, and with globalCompositeOperation, masking of shapes and text is possible, creating cut-outs in the background to make real changeable HTML elements truly transparent against a colored background. It also scales well, and can easily be made responsive.
The canvas element is supported in all major browsers except Internet Explorer 8 and below, which means browser support is better than many of the CSS3 methods previously mentioned, like keyframes and background-size.
Using a fallback, like say images that fade in and out if canvas is'nt available, should'nt be very hard to figure out, and in all other browsers except Internet Explorer below version 9, no images would be needed to create the gradient backgrounds and text masks in a canvas, which should make the loading of the page significantly faster.
To detect wether or not canvas is supported, you can use this convenient function :
function isCanvasSupported(){
var elem = document.createElement('canvas');
return !!(elem.getContext && elem.getContext('2d'));
}
used like so :
if ( isCanvasSupported() ) {
// do canvas stuff
}else{
// fall back to images
}
So, lets get to it! To create a "last resort" fallback and some elements we can "clone" into the canvas, we'll create the elements we need in the HTML to get a structure somewhat similar to what you've outlined in your question. This has the added advantage of being able to just change some of the CSS to also make changes in the canvas :
<div id="gradient">
<div class="text">COMPANY NAME</div>
<div class="h_bar"></div>
<div class="v_bar"></div>
</div>
It's just a container with an element for text, and one for each of the bars.
Some styling is neccessary as well, I'll do it the easy way, with position absolute and some really fast positioning, as these elements won't be visible unless someone has disabled javascript anyway :
#gradient {position: absolute;
background: #000;
top: 5%; left: 5%; right: 5%; bottom: 5%;
}
.text {position: absolute;
top: 20px;
left: 100px;
width: 400px;
color: #fff; font-size: 40px; font-weight: bold;
font-family: arial, verdana, sans-serif;
}
.h_bar {position: absolute;
height: 20px;
top: 100px; left: 60px; right: 60px;
background: #fff;
}
.v_bar {position: absolute;
width: 20px;
top: 140px; bottom: 30px; right: 60px;
background: #fff;
}
Without any javascript that would look exactly like THIS FIDDLE, and it should be somewhat responsive and adapt to the window size.
Now we need some javascript to turn those elements into something in a canvas. We'll create two canvas elements, one for the background, as I've decided to animate the background continously between random gradients, and one for the inner black box and the content (the text and the bars).
As the masking of the text and bars can be a little slow, we don't have to redraw everything, just the background canvas, as the foreground is pretty static.
This also avoids a flickering issue in some browsers with high frame rates, and we're going to use requestAnimationFrame for the animation of the background canvas, so flickering in the text mask would be an issue if we did'nt use two canvas elements.
For browsers that does'nt support requestAnimationFrame we'll add this polyfill to make sure it works everywhere.
Time to write some javascript, this of course uses jQuery :
var gradSite = {
init: function() {
var self = this;
self.create().setSizes().events();
(function animationloop(){
requestAnimationFrame(animationloop);
self.draw().colors.generate();
})();
},
create: function() { // creates the canvas elements
this.canvas = document.createElement('canvas');
this.canvas2 = document.createElement('canvas');
this.canvas.id = 'canvas1';
this.canvas2.id = 'canvas2';
this.canvas.style.position = 'absolute';
this.canvas2.style.position = 'absolute';
$('#gradient').after(this.canvas, this.canvas2);
return this;
},
events: function() { //event handlers
$(window).on('resize', this.setSizes);
$('#gradient').on('contentchange', this.draw2);
return this;
},
setSizes: function() { // sets sizes on load and resize
var self = gradSite,
w = $(window),
m = $('#gradient');
self.canvas.height = w.height();
self.canvas.width = w.width();
self.canvas2.bg = m.css('background-color');
self.canvas2.height = m.height();
self.canvas2.width = m.width();
self.canvas2.style.top = m.offset().top + 'px';
self.canvas2.style.left = m.offset().left + 'px';
self.draw2();
return self;
},
colors: {
colors: {
0: [255,255,0],
1: [255,170,0],
2: [255,0,0]
},
map: {
0: [0,0,1],
1: [0,1,1],
2: [0,1,1]
},
generate: function() { // generates the random colors
var self = this;
$.each(self.colors, function(i,color) {
$.each(color, function(j, c) {
var r = Math.random(),
r2 = Math.random(),
val = self.map[i][j] == 0 ? (c-(j+r)) : (c+(j+r2));
if (c > 255) self.map[i][j] = 0;
if (c < 0 ) self.map[i][j] = 1;
self.colors[i][j] = val;
});
});
}
},
raf: (function() { // polyfill for requestAnimationFrame
var lastTime = 0,
vendors = ['webkit', 'moz'];
for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame'];
window.cancelAnimationFrame = window[vendors[x]+'CancelAnimationFrame'] || window[vendors[x]+'CancelRequestAnimationFrame'];
}
if (!window.requestAnimationFrame)
window.requestAnimationFrame = function(callback, element) {
var currTime = new Date().getTime(),
timeToCall = Math.max(0, 16 - (currTime - lastTime)),
id = window.setTimeout(function() { callback(currTime + timeToCall); }, timeToCall);
lastTime = currTime + timeToCall;
return id;
};
if (!window.cancelAnimationFrame)
window.cancelAnimationFrame = function(id) {
clearTimeout(id);
};
}()),
calculateColor: function(colors) { // returns a rgb color from the array
return 'rgb(' + Math.round(colors[0]) + ',' + Math.round(colors[1]) + ',' + Math.round(colors[2]) + ')';
},
draw: function() { //draws the color background
var self = this,
c = self.canvas || document.getElementById('canvas1'),
ctx = c.getContext('2d'),
grad = ctx.createLinearGradient(0,0,0,self.canvas.height);
c.width = c.width;
grad.addColorStop(0, self.calculateColor(self.colors.colors[0]));
grad.addColorStop(0.5, self.calculateColor(self.colors.colors[1]));
grad.addColorStop(1, self.calculateColor(self.colors.colors[2]));
ctx.fillStyle = grad;
ctx.fillRect(0,0,self.canvas.width, self.canvas.height);
return self;
},
draw2: function() { // draws the black square and content
var self = this,
c = self.canvas2 || document.getElementById('canvas2'),
ctx2 = c.getContext('2d'),
txt = $('.text', '#gradient').first(),
hbar = $('.h_bar', '#gradient').first(),
vbar = $('.v_bar', '#gradient').first();
c.width = c.width;
ctx2.globalCompositeOperation = 'xor';
ctx2.font = txt.css('font');
ctx2.fillStyle = c.bg || '#000';
ctx2.fillText(txt.text(), txt.offset().left, txt.offset().top);
ctx2.fillRect(hbar.position().left, hbar.position().top, hbar.width(),hbar.height());
ctx2.fillRect(vbar.position().left, vbar.position().top, vbar.width(),vbar.height());
ctx2.fillRect(0,0,c.width,c.height);
}
}
The raf function would be the polyfill for requestAnimationFrame, and the two draw functions create the content in the canvas. It's really not that complicated.
We will call the above script inside a DOM ready handler, like so :
$(function() {
gradSite.init(); // starts the canvas stuff
});
Adding all that up into a fiddle, and adding a few elements for demonstration purposes, it would look like THIS FIDDLE, and here's the finished ->
FULL SCREEN DEMO
The only way I can see this working is if your black div has no background and is cut into sections that that each have a background. The company name area would need to have the same foreground color as the background for the rest of the div sections. Depending on your layout needs this might be fine.
For example, you could cut it into three sections and two images:
You can try combinig background-size and background-position with javascript:
setGradientSizes = function (el) {
var width = $(document).width() + 'px', height = $(document).height() + 'px';
$(el || '.gradient:not(body)').each(function () {
var offset = $(this).offset();
$(this).css('background-size', width + ' ' + height);
$(this).css('background-position', (offset.left * -1) + 'px ' + (offset.top * -1) + 'px');
})};
Working example here -> jsbin
NOTES:
this is not 100% cross browser - background-size is supported in FF4.0+, IE9.0+, Opera 10.0+, Chrome 1.0+, Safari 3+.
For some older browsers you can try browser specific prefixes (like -moz-background-size) - my example does not cover that.
To reduce load flickering you can apply calculations at first and then add background gradient
You could make the background of the image with the text black, then set the div's background color to rgba(0,0,0,0) making it transparent
This might be helpful for you according to my understanding
There is inherit to copy a certain value from a parent to its children, but there is no property the other way round (which would involve another selector to decide which style to revert).
You will have to revert style changes manually:
div { color: green; }
form div { color: red; }
form div div.content { color: green; }
If you have access to the markup, you can add several classes to style precisely what you need:
form div.sub { color: red; }
form div div.content { /* remains green */ }
Edit: The CSS Working Group is up to something:
div.content {
all: default;
}
If I was you I'll duplicate the css and jQuery, print it on a div on top of what ever and make the overflow hidden (like masking layers but with z-index).

Changing background color opacity on mouseover

I have a DIV that I'd like to change the background color opacity on, depending on if the mouse is over it or not.
I know you can use background: rgba(54, 25, 25, .5) etc, but I want to set the colour separately. Is there any way I can JUST modify the OPACITY, and not the colour.
I could opacity: 0.3, etc, but that effects the whole DIV, and I just want to affect the background colour.
No html/css doesn't have that option built in, but since you're accessing/setting the colour in javascript you might as well add in your own function which can handle that for you.
Here's an example for you:
<script type="text/javascript">
function RGBA(red,green,blue,alpha) {
this.red = red;
this.green = green;
this.blue = blue;
this.alpha = alpha;
this.getCSS = function() {
return "rgba("+this.red+","+this.green+","+this.blue+","+this.alpha+")";
}
}
// store a copy of the color
var bgColor = new RGBA(255,0,0,0.5);
function setBgOpacity(elem, opac) {
bgColor.alpha = opac;
elem.style.backgroundColor = bgColor.getCSS();
}
</script>
Then in the HTML use the onmouseover event to change the opacity of the bgColor:
<div onmouseover="setBgOpacity(this, '0.3');"
onmousout="setBgOpacity(this, '0.5');">Put your mouse over me</div>
You can make the background part of a different div and set the opacity of THAT div, i.e.
<div id="container">
<div id="background"></div>
<div id="content">
<p>Lorum ipsum...</p>
</div>
</div>
And
#container { overflow:hidden; position:relative; }
#background {
position:absolute;
top:0;
left:0;
width:100%;
height:100%;
background:#FF0000;
}
#background:hover { opacity:0.3; }
#content { position:relative; z-index:10; }
There a difference between the Alpha value in RGBa and Opacity. Opacity affects all child elements, Alpha does not.
You'll have to read the current colour value, then restate it as RGBa with the new Alpha value. You may need to convert the current hex colour value to a decimal triplet to do this.
If you are relying on RGBA to modify the opacity of the background color, no, there is no way to set that separately from the color itself. You will have to declare explicit RGBA values for both your normal and hover states.
No, you can't edit only the alpha of rgba. So you should use the RGB part of the RGBa.
If you want a separate background colour from the container you may want to use :before or :after.
.container {
position: relative;
&:before {
content: '';
position: absolute;
width: 100%;
height: 100%;
background-color: #000;
opacity: 1;
z-index: -1;
}
&:hover {
&:before {
opacity: 0.5;
}
}
.content {
z-index: 1;
}
}
When you hover on the .container, only the opacity of the :before is effected and not the contents.

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